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Alcohols

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Intros
Lessons
  1. Alcohols - Introduction
  2. Definition and structure of alcohols.
  3. Properties and uses of alcohols.
  4. Types of alcohols.
  5. Testing for alcohols.
  6. Naming alcohols.
  7. Reactions of alcohols
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Examples
Lessons
  1. Recall the general formula of an alcohol.
    Study the following molecular formulae and determine which of them are alcohols.
    i) C3_3H8_8OH
    ii) C4_4H10_{10}O
    iii) C5_5H11_{11}OH
    iv) C8_8H18_{18}OH
    1. Recall simple alcohols, their properties and the trends in properties.
      1. Organise the following alcohols in order of their solubility in water.

        i) Methanol
        ii) Pentanol
        iii) Hexanol
        iv) Butanol
        v) Ethanol
      2. Explain why alcohols dissolve in water but alkanes do not.
    Topic Notes
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    Introduction to Alcohols

    Alcohols are a fundamental functional group in organic chemistry, characterized by the presence of a hydroxyl (-OH) group attached to a carbon atom. The introduction video provides a comprehensive overview of alcohols, serving as a crucial starting point for understanding this important class of compounds. Alcohols exhibit unique properties due to their molecular structure, making them essential in various chemical reactions and industrial applications. The alcohol definition in chemistry encompasses a wide range of molecules, from simple methanol to complex organic chemistry compounds. It's important to note that while alcoholic beverages contain ethanol, not all alcohols are suitable for consumption. Is alcohol a compound? Yes, alcohols are indeed organic compounds with distinct chemical and physical properties. Their ability to form hydrogen bonds contributes to their solubility in water and higher boiling points compared to similar-sized hydrocarbons. Understanding alcohols is crucial for students and professionals in chemistry, biology, and related fields.

    Structure and Classification of Alcohols

    Alcohols are a class of organic compounds characterized by their unique structure, which sets them apart from other organic molecules. The defining feature of an alcohol is the presence of a hydroxyl group (-OH) attached to a carbon atom. This hydroxyl group is responsible for many of the distinctive properties of alcohols, including their polarity and ability to form hydrogen bonds. To understand alcohols better, it's essential to explore their general structure, classification, and how they differ from hydrocarbons like alkanes.

    The general structure of an alcohol consists of an alkyl group (R-) bonded to a hydroxyl group (-OH). The alkyl group can be a simple methyl group (CH3-) or a more complex carbon chain. The hydroxyl group is the key component that defines an alcohol and gives it its characteristic properties. This structure can be represented as R-OH, where R represents the alkyl group.

    Alcohols are classified into three main categories based on the number of carbon atoms attached to the carbon bearing the hydroxyl group:

    1. Primary alcohols: The carbon atom with the -OH group is attached to only one other carbon atom.
    2. Secondary alcohols: The carbon atom with the -OH group is attached to two other carbon atoms.
    3. Tertiary alcohols: The carbon atom with the -OH group is attached to three other carbon atoms.

    This classification is important because it affects the reactivity and properties of the alcohol. For example, primary alcohols are generally more reactive than secondary or tertiary alcohols in oxidation reactions.

    A common question that arises is, "Is ethanol a hydrocarbon?" The answer is no, ethanol is not a hydrocarbon. Hydrocarbons are compounds composed only of carbon and hydrogen atoms. Alcohols, including ethanol, contain oxygen in addition to carbon and hydrogen, which disqualifies them from being classified as hydrocarbons. This distinction is crucial in understanding the properties and behavior of alcohols compared to hydrocarbons.

    Ethanol (CH3CH2OH) serves as an excellent example to illustrate these concepts. It is a primary alcohol because the carbon atom bearing the hydroxyl group is attached to only one other carbon atom. The presence of the -OH group in ethanol gives it properties that are distinctly different from those of its alkane counterpart, ethane (CH3CH3). For instance, ethanol is more polar, has a higher boiling point, and is soluble in water, unlike ethane.

    The question "Is alcohol a hydrocarbon?" can be definitively answered: no, alcohols are not hydrocarbons. While both alcohols and hydrocarbons contain carbon and hydrogen, the presence of oxygen in alcohols sets them apart. This oxygen atom in the hydroxyl group is responsible for many of the unique properties of alcohols, such as their ability to form hydrogen bonds and their increased polarity compared to hydrocarbons.

    To address the query "Is ethanol a primary alcohol?", the answer is yes. Ethanol fits the definition of a primary alcohol perfectly, as the carbon atom bearing the hydroxyl group is attached to only one other carbon atom. This classification affects ethanol's reactivity and properties, making it more susceptible to oxidation compared to secondary or tertiary alcohols.

    In conclusion, understanding the structure and classification of alcohols is fundamental in organic chemistry. The presence of the hydroxyl group, the classification into primary, secondary, and tertiary alcohols, and the distinction from hydrocarbons are key concepts. Ethanol serves as a prime example of a primary alcohol, illustrating these principles and highlighting the unique properties that set alcohols apart from their hydrocarbon counterparts.

    Properties of Alcohols

    Alcohols are a class of organic compounds that play a significant role in chemistry and everyday life. To understand their importance, it's crucial to explore their key properties and how they differ from other hydrocarbons. While alcohols are not strictly hydrocarbons due to the presence of oxygen, they share some similarities with their hydrocarbon counterparts.

    The defining feature of alcohols is the hydroxyl group (-OH) attached to a carbon atom. This functional group is responsible for many of the unique properties that set alcohols apart from alkanes and other hydrocarbons. The alcohol definition in chemistry emphasizes this structural characteristic, which gives rise to their distinct behavior and applications.

    One of the most notable properties of alcohols is their solubility in water. Unlike alkanes, which are generally insoluble in water, alcohols can form hydrogen bonds with water molecules. This ability to interact with water makes many alcohols miscible or highly soluble in aqueous solutions. The degree of solubility typically decreases as the carbon chain length increases, with lower molecular weight alcohols like methanol and ethanol being completely miscible with water.

    The boiling points of alcohols are generally higher than those of alkanes with similar molecular weights. This is due to the strong hydrogen bonding between alcohol molecules, which requires more energy to overcome during the vaporization process. As the carbon chain length increases, the boiling point also rises, but the effect of the hydroxyl group becomes less pronounced relative to the overall molecular size.

    Polarity is another key characteristic of alcohols. The presence of the electronegative oxygen atom in the hydroxyl group creates a dipole moment, making alcohols polar molecules. This polarity contributes to their solubility in water and other polar solvents, as well as their ability to dissolve many ionic compounds. In contrast, alkanes are non-polar and do not exhibit these properties.

    The hydroxyl group's influence extends beyond solubility and polarity. It also affects the reactivity of alcohols, making them more versatile in chemical reactions compared to alkanes. Alcohols can participate in various reactions, including oxidation, dehydration, and esterification, which are not typical for alkanes.

    When comparing alcohols to alkanes, several differences become apparent. While alkanes are relatively inert and non-polar, alcohols are more reactive and polar. Alkanes are excellent fuels due to their high energy content and clean combustion, but alcohols, particularly ethanol, have also found use as alternative fuels or fuel additives.

    Flammability is a property shared by both alcohols and alkanes, but with some distinctions. Alcohols, especially those with lower molecular weights, are highly flammable. Ethanol, for example, has a flash point of about 13°C (55°F), making it easily ignitable at room temperature. This flammability has led to the use of alcohols in applications such as fuel and disinfectants.

    Regarding toxicity, alcohols generally exhibit lower acute toxicity compared to many hydrocarbons. However, they can still pose health risks, particularly when ingested or inhaled in large quantities. Ethanol, the alcohol found in alcoholic beverages, serves as a prime example. While it has relatively low toxicity compared to other alcohols, excessive consumption can lead to intoxication, impaired judgment, and long-term health issues.

    In conclusion, the properties of alcohols, including their solubility, boiling points, polarity, flammability, and toxicity, are largely influenced by the presence of the hydroxyl group. These characteristics distinguish alcohols from alkanes and other hydrocarbons, making them valuable in various applications ranging from solvents and fuels to pharmaceuticals and personal care products. Understanding these properties is essential for anyone studying chemistry or working with these versatile compounds.

    Nomenclature of Alcohols

    The IUPAC (International Union of Pure and Applied Chemistry) naming system for alcohols provides a standardized method for naming these important organic chemistry compounds. Understanding this system is crucial for chemists and students alike, as it allows for clear communication about chemical structures. Let's explore the key principles of naming alcohols and practice applying them.

    Alcohols are organic chemistry compounds characterized by the presence of a hydroxyl (-OH) group attached to a carbon atom. The alcohol definition in chemistry emphasizes this distinctive functional group. When naming alcohols, we follow these general steps:

    1. Identify the longest carbon chain containing the -OH group.
    2. Number the chain, starting from the end closest to the -OH group.
    3. Name the parent chain, replacing the "-e" ending with "-ol".
    4. Indicate the position of the -OH group using the appropriate number.
    5. Add prefixes for any substituents, listing them alphabetically.

    Let's look at some examples to illustrate these principles:

    • CH3CH2OH: ethanol (simple alcohol)
    • CH3CH(OH)CH3: propan-2-ol (isopropyl alcohol)
    • CH3CH2CH2CH2OH: butan-1-ol

    In more complex alcohols, it's crucial to indicate the position of the hydroxyl group. For instance:

    • CH3CH(CH3)CH(OH)CH2CH3: 3-methylpentan-3-ol
    • (CH3)3CCH2OH: 2,2-dimethylpropan-1-ol

    The question "Is ethanol a primary alcohol?" can be answered by examining its structure. Ethanol (CH3CH2OH) is indeed a primary alcohol because the -OH group is attached to a carbon that is bonded to only one other carbon atom.

    To reinforce your understanding, try naming these alcohols:

    1. CH3CH2CH(OH)CH3
    2. (CH3)2CHCH2CH(OH)CH3
    3. CH3CH(CH3)CH(OH)CH2CH2CH3

    Answers: 1. butan-2-ol, 2. 4-methylpentan-2-ol, 3. 3-methylhexan-3-ol

    Mastering the IUPAC naming system for alcohols is essential for anyone studying organic chemistry. It provides a clear, unambiguous way to describe these compounds, which are ubiquitous in both natural and synthetic contexts. From simple alcohols like ethanol to more complex structures, this naming convention ensures that chemists worldwide can communicate effectively about these important molecules.

    Reactions of Alcohols

    Alcohols are versatile organic compounds that play a crucial role in chemistry. To understand their behavior, it's essential to explore the common reactions of alcohols and how their structure affects their reactivity. This discussion will focus on the oxidation of alcohols, their reactions with alkali metals and acids, and the differences in reactivity between primary, secondary, and tertiary alcohols.

    Oxidation is one of the most important reactions of alcohols. The process involves the loss of hydrogen atoms and the gain of oxygen atoms. The extent of oxidation depends on the type of alcohol:

    • Primary alcohols (R-CH2OH) can be oxidized to aldehydes (R-CHO) and further to carboxylic acids (R-COOH).
    • Secondary alcohols (R2CHOH) oxidize to ketones (R2CO).
    • Tertiary alcohols (R3COH) are resistant to oxidation under normal conditions.

    For example, ethanol, which is a primary alcohol, can be oxidized to ethanal (acetaldehyde) and then to ethanoic acid (acetic acid):

    CH3CH2OH CH3CHO CH3COOH

    Alcohols react vigorously with alkali metals such as sodium and potassium. This reaction produces a metal alkoxide and hydrogen gas. The general equation for this reaction is:

    2R-OH + 2Na 2R-ONa + H2

    For instance, ethanol reacts with sodium to form sodium ethoxide:

    2CH3CH2OH + 2Na 2CH3CH2ONa + H2

    Alcohols also react with acids, particularly strong acids, in a process called esterification. This reaction produces esters and water. The general equation is:

    R-OH + R'-COOH R-COO-R' + H2O

    For example, ethanol reacts with ethanoic acid to form ethyl ethanoate:

    CH3CH2OH + CH3COOH CH3COOCH2CH3 + H2O

    The reactivity of alcohols varies significantly depending on whether they are primary, secondary, or tertiary. This difference is particularly noticeable in oxidation reactions:

    • Primary alcohols are the most reactive. They can be oxidized to aldehydes and then to carboxylic acids. For instance, ethanol (CH3CH2OH) is a primary alcohol that readily oxidizes.
    • Secondary alcohols are less reactive than primary alcohols. They oxidize to ketones but do not form carboxylic acids. An example is 2-propanol (CH3CH(OH)CH3), which oxidizes to propanone (acetone).
    • Tertiary alcohols are the least reactive. They resist oxidation under normal conditions due to the absence of a hydrogen atom on the carbon bearing the -OH group.

    The reactivity differences also manifest in other reactions. For example, in the reaction with hydrogen halides (HX), the order of reactivity is tertiary > secondary > primary. This is because the reaction proceeds through a carbocation intermediate, which is most stable for tertiary alcohols.

    Alcohols react vigorously with alkali metals such as sodium and potassium. This reaction produces a metal alkoxide and hydrogen gas. The general equation for this reaction is:

    Applications and Importance of Alcohols

    Alcohols play a crucial role in various aspects of our lives, from industry and medicine to everyday products. These versatile compounds, characterized by the presence of a hydroxyl (-OH) group, have a wide range of applications due to their unique properties. To answer a common question: no, ethanol is not a hydrocarbon, as it contains oxygen in addition to carbon and hydrogen. The alcohol definition in chemistry refers to any organic compound with a hydroxyl group attached to a carbon atom.

    In industry, alcohols serve numerous purposes. Methanol, the simplest alcohol, is used as a solvent and in the production of biodiesel. Ethanol, perhaps the most well-known alcohol, has extensive industrial applications. It's used as a fuel additive, enhancing octane ratings and reducing carbon monoxide emissions. Ethanol is also a key ingredient in the production of plastics, synthetic rubber, and various chemicals. Higher alcohols like propanol and butanol are important in the manufacturing of paints, varnishes, and cosmetics.

    The medical field heavily relies on alcohols, particularly ethanol. It's a primary component in hand sanitizers and disinfectants, crucial for maintaining hygiene in healthcare settings. Isopropyl alcohol (rubbing alcohol) is widely used for sterilizing medical equipment and as an antiseptic. In pharmaceuticals, alcohols serve as solvents for many medications and are used in the synthesis of various drugs.

    In everyday life, we encounter alcohols more often than we might realize. Ethanol is the type of alcohol found in alcoholic beverages. It's also used in perfumes, as a preservative in some food products, and in many household cleaning products. Other alcohols are found in personal care items like mouthwashes, deodorants, and hair sprays.

    Ethanol deserves special mention due to its significance. Beyond its industrial and medical applications, it's a key player in the renewable energy sector. As a biofuel, ethanol offers a more environmentally friendly alternative to fossil fuels, reducing greenhouse gas emissions. Its production from crops like corn and sugarcane also supports agricultural economies.

    In organic synthesis, alcohols are invaluable. They serve as precursors for many other organic compounds. Through various reactions like oxidation, dehydration, and esterification, alcohols can be transformed into aldehydes, ketones, alkenes, and esters. This versatility makes them essential building blocks in the chemical industry for producing a vast array of products.

    The significance of alcohols in biochemistry cannot be overstated. They are integral to many biological processes. For instance, cholesterol, a type of alcohol, is crucial for cell membrane structure and hormone production. Sugars, which are polyhydroxy alcohols, are fundamental to energy metabolism. The enzyme alcohol dehydrogenase, which breaks down ethanol in our bodies, plays a vital role in alcohol metabolism.

    In conclusion, alcohols, especially ethanol, are indispensable in modern life. Their applications span across industries, medicine, and daily products, making them one of the most important classes of organic compounds. Understanding alcohols is key to appreciating their role in chemistry, biology, and our everyday experiences.

    Conclusion

    Alcohols are vital compounds in organic chemistry, defined by their hydroxyl (-OH) group attached to a carbon atom. This unique structure gives alcohols distinct properties, including hydrogen bonding capabilities and varying levels of solubility. The alcohol definition in chemistry encompasses a wide range of molecules, from simple methanol to complex sugars. Is alcohol a compound? Absolutely. These versatile substances play crucial roles in numerous applications, from industrial processes to biological systems. The introduction video provided a foundation for understanding alcohols, highlighting their structure, nomenclature, and basic properties. As we've explored, alcohols exhibit fascinating behaviors in reactions, serving as both nucleophiles and electrophiles. Their importance in organic synthesis, fuel production, and everyday products cannot be overstated. We encourage you to delve deeper into alcohol chemistry, exploring topics like oxidation reactions, esterification, and the role of alcohols in biochemistry. The world of alcohols is rich with possibilities, waiting to be discovered.

    Alcohols - Introduction

    Alcohols - Introduction Definition and structure of alcohols.

    Step 1: Understanding Alcohols as a Functional Group

    Alcohols are a type of functional group in organic chemistry. A functional group is a specific group of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. In the case of alcohols, the functional group is the hydroxyl group (OH). This group is what defines alcohols and gives them their unique properties.

    Step 2: General Formula and Structure of Alcohols

    The general formula for alcohols is CNH2N+2O. This formula is similar to that of alkanes (which is CNH2N+2) but with an additional oxygen atom. The presence of the hydroxyl group (OH) is crucial as it differentiates alcohols from other hydrocarbons. For example, if you take an alkane and replace one hydrogen atom with a hydroxyl group, you get an alcohol.

    Step 3: Comparing Alcohols to Alkanes

    To understand alcohols better, it helps to compare them to alkanes. Alkanes are simple hydrocarbons consisting only of carbon and hydrogen atoms. If you remove the oxygen atom from an alcohol, you would be left with an alkane. For instance, if you have a molecule with a carbon chain and a hydroxyl group, removing the hydroxyl group would leave you with a simple alkane.

    Step 4: The Hydroxyl Group

    The hydroxyl group (OH) is the defining feature of alcohols. It is what makes alcohols behave and react the way they do. Unlike hydrocarbons, which consist only of hydrogen and carbon, alcohols contain an oxygen atom. This oxygen atom is bonded to a hydrogen atom, forming the hydroxyl group. The presence of this group is what makes alcohols distinct from other types of organic compounds.

    Step 5: Naming Alcohols Using IUPAC Nomenclature

    Alcohols are named using the IUPAC (International Union of Pure and Applied Chemistry) nomenclature system. The name of an alcohol is derived from the name of the corresponding alkane by replacing the 'e' at the end with 'ol'. For example, the alcohol derived from ethane is called ethanol (C2H5OH). Similarly, the alcohol derived from propane is called propanol. This systematic naming helps in identifying and categorizing different alcohols.

    Step 6: Example of an Alcohol - Ethanol

    Let's take ethanol as an example. Ethanol has the chemical formula C2H5OH. It consists of two carbon atoms, six hydrogen atoms, and one hydroxyl group. If you were to remove the hydroxyl group, you would be left with ethane (C2H6), a simple alkane. The presence of the hydroxyl group is what makes ethanol an alcohol. The name 'ethanol' is derived from 'ethane' by replacing the 'e' at the end with 'ol'.

    Step 7: Importance of Writing the Formula Correctly

    When writing the chemical formula of an alcohol, it is important to include the hydroxyl group explicitly. For example, ethanol should be written as C2H5OH rather than C2H6O. This is because writing the formula as C2H6O can be confusing and may be mistaken for another functional group. Including the hydroxyl group in the formula helps in clearly identifying the compound as an alcohol.

    Step 8: Summary

    In summary, alcohols are a type of functional group in organic chemistry characterized by the presence of a hydroxyl group (OH). They have a general formula of CNH2N+2O and are named using the IUPAC nomenclature system by replacing the 'e' at the end of the corresponding alkane with 'ol'. The hydroxyl group is what gives alcohols their unique properties and differentiates them from other hydrocarbons. Understanding the structure and naming of alcohols is crucial for studying their properties and reactions in organic chemistry.

    FAQs

    Here are some frequently asked questions about alcohols:

    1. Is ethanol a hydrocarbon or not?

      No, ethanol is not a hydrocarbon. While it contains carbon and hydrogen atoms, it also has an oxygen atom in its hydroxyl (-OH) group. Hydrocarbons consist only of carbon and hydrogen atoms.

    2. Are alcohols hydrocarbons?

      No, alcohols are not hydrocarbons. Alcohols contain a hydroxyl (-OH) group, which includes an oxygen atom. Hydrocarbons, by definition, only contain carbon and hydrogen atoms.

    3. What is the classification of alcohol?

      Alcohols are classified into three main types based on the number of carbon atoms attached to the carbon bearing the hydroxyl group: primary (1°), secondary (2°), and tertiary (3°) alcohols.

    4. Is ethanol a primary or secondary alcohol?

      Ethanol (CH3CH2OH) is a primary alcohol. The carbon atom bearing the hydroxyl group is attached to only one other carbon atom, which defines it as a primary alcohol.

    5. What is alcohol considered in chemistry?

      In chemistry, alcohol is considered an organic compound characterized by a hydroxyl (-OH) group attached to a carbon atom. Alcohols are versatile compounds with various applications in industry, medicine, and everyday life.

    Prerequisite Topics for Understanding Alcohols

    When delving into the study of alcohols in organic chemistry, it's crucial to have a solid foundation in certain prerequisite topics. These fundamental concepts provide the necessary groundwork for comprehending the complex nature and behavior of alcohols. Two key areas that are particularly relevant are arrow pushing (curly arrows) in organic chemistry and understanding the properties of Group 1 and Group 2 alkali and alkaline earth metals.

    Mastering the concept of arrow pushing in organic chemistry is essential when studying alcohols. This technique is instrumental in visualizing and predicting the movement of electrons during chemical reactions involving alcohols. The hydroxyl group, which is characteristic of alcohols, plays a pivotal role in many organic reactions. By understanding how to use curly arrows to represent electron flow, students can better grasp the mechanisms behind alcohol-related reactions, such as oxidation, dehydration, and esterification.

    Moreover, the ability to accurately depict electron movement helps in comprehending the formation and breaking of bonds in alcohol molecules. This skill is particularly useful when exploring the reactivity of alcohols with various compounds and in different chemical environments. The arrow pushing technique allows students to track the fate of electrons throughout a reaction, providing insights into why certain products are formed and others are not.

    Equally important is the knowledge of Group 1 and Group 2 elements, also known as alkali and alkaline earth metals. These metals exhibit distinctive reactivity patterns with alcohols, which is crucial for understanding alcohol chemistry. The reactivity of alcohols with alkali metals is a classic example of how the hydroxyl group behaves in certain chemical reactions. This interaction demonstrates the acidic nature of alcohols and the formation of alkoxides, which are important intermediates in many organic syntheses.

    Understanding the properties of these metals helps explain why alcohols react more vigorously with sodium and potassium compared to less reactive metals. This knowledge is not only important for laboratory safety but also for predicting and explaining the outcomes of reactions involving alcohols and metal catalysts or reagents.

    By mastering these prerequisite topics, students build a strong conceptual framework for studying alcohols. The ability to visualize electron movement and understand metal reactivity provides a deeper insight into the chemical behavior of alcohols. This foundation enables students to tackle more advanced concepts in alcohol chemistry, such as oxidation states, nucleophilic substitution reactions, and the synthesis of more complex organic compounds.

    In conclusion, a thorough grasp of arrow pushing techniques and the chemistry of alkali and alkaline earth metals significantly enhances one's understanding of alcohol chemistry. These prerequisite topics serve as building blocks, allowing students to construct a comprehensive knowledge of alcohols, their properties, and their reactions in organic chemistry.

    In this lesson, we will learn:
    • The definition and general formula of an alcohol with some basic examples.
    • The major properties of alcohols and their difference to the hydrocarbons.
    • The reactions of alcohols and how the type of alcohols affects reactivity.
    • How to name alcohols using IUPAC organic nomenclature.

    Notes:
    • Alcohols are another homologous series: a "family" of organic molecules with the same general formula, each member differing from the next by a -CH2- hydrocarbon chain unit.
      Any organic compound where the hydroxyl (-OH) group is covalently bonded to a saturated carbon atom is an alcohol.
      The -OH hydroxyl group is the functional group that makes an alcohol react the way it does. A molecule must have a carbon atom with four single bonds, one to an OH group, to be called an alcohol.

    • Unlike alkanes, alkenes and alkynes, alcohols are not hydrocarbons. They are not considered hydrocarbons because alcohols contain an oxygen atom in the molecule.

    • Alkanes have the general formula: CnH2n+2O but it is normally written as CnH2n+1OH, to show the hydroxyl group that defines an alcohol. Alcohols then are very similar to alkanes of the same carbon chain length; there is same number of carbons and hydrogens, just with an extra oxygen atom.
      This is because a hydroxyl group is just an oxygen atom bonded to a hydrogen atom, making one bond to the rest of the molecule through a carbon atom. Naming of simple alcohols is very similar to alkanes as a result; alcohols have the suffix ol instead of -e in alkanes and alkenes. See the table below for the names of some simple alcohols.

      • Carbon chain length

      Name of alcohol

      Molecular formula

      1

      Methanol

      CH3OH

      2

      Ethanol

      C2H5OH

      3

      Propanol

      C3H7OH

      4

      Butanol

      C4H9OH



    • Alcohols are important solvents in chemistry. They are used to dissolve other chemicals. The most generally used alcohol is ethanol, C2_2H5_5OH which is used as a fuel and is the alcohol used in alcoholic drinks.

    • Despite being quite similar in structure to basic alkanes, the properties of alcohols are very different from alkanes. The OH group means hydrogen bonding exists between separate alcohol molecules, which affects their melting/boiling points and solubility. Oxygen is a very electronegative atom with two lone pairs, which the hydrogen atom of OH groups in other molecules can interact with.
      The major properties of alcohols are:
      • A much higher melting and boiling point than the alkanes of the same chain length. Methanes boiling point is around -164°C, while methanols boiling point is around 60°C.
      • Polarity: shorter alcohols are polar molecules that dissolve in water, not fats. The longer the chain, the less mixable with water they are.
      • Toxic: all alcohols are toxic, including ethanol found in alcoholic drinks (drunkenness is also known as intoxication!).
      • Flammable: alcohols burn with a relatively clean flame compared to alkanes and do not produce soot (carbon particulates).

    • There are clear trends in their properties. These property trends can be explained by intermolecular forces. As the carbon chain length of alcohols gets longer, they:
      • Have a higher melting/boiling point. As the carbon chain gets longer there is yet more van der Waals around it as other carbon chains can align with it, so MP/BP increases accordingly.
      • Are less volatile / flammable. The longer chain alcohols have a lower tendency to vaporize with greater IMFs between the molecules.
      • Are less soluble in water. The longer carbon chain makes the molecule more hydrophobic in general, so they do not mix with water as well as the shorter alcohols. Ethanol is highly soluble in water but hexanol is not.

    • Depending on the carbon atom the hydroxyl OH group is bonded to, we can describe three types of alcohols. There are also chemical tests to determine which one we have. Testing for the presence of alcohol compounds involves using acidified potassium dichromate.
      • A primary alcohol (1°) is an alcohol with the –OH group bonded to a carbon atom making only one carbon-carbon bond. This would place the –OH group at the end of a carbon chain.
      • A secondary alcohol (2°) is an alcohol with the –OH bonded to a carbon atom making two carbon-carbon bonds. This would place the –OH group in the middle of a carbon chain.
      • A tertiary alcohol (3°) is an alcohol where the –OH group bonds to a carbon atom with three carbon-carbon bonds. This would place the –OH group on a carbon where a branch in the carbon chain is found. See the table (the brackets in the middle column show branching) and examples.

      Type of alcohol

      C-OH bonding:

      Test to identify using:

      1. Acidified potassium dichromate.

      2. Acidified silver nitrate to the product of 1.

      Primary (1o)

      -CH2OH

      1. Solution changes colour from orange to green.

      2. Silver mirror is observed in the test tube.

      Secondary (2o)

      -CH(OH)-

      1. Solution changes colour from orange to green.

      2. Add acidified silver nitrate – no observed change.

      Tertiary (3o)

      -C(C)(OH)-

      1. No observed change. Orange solution stays orange.



      types of alcohol


    • Alcohols are known to perform a number of reactions:
      • Alcohols react with alkali metals to form metal salts and hydrogen gas. The reaction with sodium is:

        • 2C2_2H5_5OH + 2Na   \, →  \, 2C2_2H5_5ONa + H2_2

      • Alcohols also react with acids to form alkyl halides and water as a side product. The reaction with hydrochloric acid is:

        • C2_2H5_5OH + HCl   \, →  \, C2_2H5_5Cl + H2_2O


      • As mentioned above, alcohols can be burned easily like alkanes and alkenes, but they burn more cleanly. This means more complete combustion occurs so less soot (carbon particulates) and CO is made. For example, with ethanol:

        • C2H5OH + 3 O2   \, →  \, 2 CO2 + 3H2O

      • Alcohols can be oxidized into aldehydes or ketones, depending on the type.
        We usually represent the oxidizing agent with an [O] in the chemical equation, so the focus stays on the organic substance. [O] just means it supplies oxygen to the other substance. Primary alcohols will be oxidized to aldehydes, and secondary alcohols will be oxidized to ketones. Tertiary alcohols cannot be oxidized. The oxidation of ethanol to ethanol is shown below:

        • C2_2H5_5OH + [O]   \, →  \, C2_2H4_4O + H2_2O

      • Primary alcohols can be oxidized straight to carboxylic acids, skipping the aldehyde step in between. Remember that ketones cannot be reacted to make carboxylic acids, only aldehydes can. The full oxidation of ethanol is below:

        • C2_2H5_5OH + 2[O]   \, →  \, H3_3CCOOH + H2_2O

      • In most cases when the aldehyde is produced, it will react further and make the carboxylic acid in the last equation above. For this reason, the reaction is often done under reflux with distillation to separate the two products the aldehyde and the carboxylic acid.

    • To name alcohols using IUPAC nomenclature, the –OH group is given the suffix –ol. It is also given a number to show which carbon atom in the main chain it is bonded to.
      • All the systematic rules of naming alkanes, alkyl branches and alkenes apply.
      • Alcohol groups are higher order (priority) than alkenes and alkyl branches, so numbering prioritizes alcohol groups.