Classification Of Organic Compounds PDF

# Classification of organic compounds ## 1. General Principles All organic molecules include a backbone constructed from the elements carbon and hydrogen. Many organic molecules also include one or more functional groups, structural motifs conferring specific chemical properties that consist of spe...

# Classification of organic compounds ## 1. General Principles All organic molecules include a backbone constructed from the elements carbon and hydrogen. Many organic molecules also include one or more functional groups, structural motifs conferring specific chemical properties that consist of specific groups of bonded atoms. Because molecules having the same functional group often react in similar ways, organic chemists find it useful to classify organic compounds by functional group. ## 2. Classes of organic compounds ### a) Hydrocarbons Hydrocarbons contain only carbon and hydrogen. A hydrocarbon is said to be saturated if its only contains single bonds and unsaturated if it has at least one multiple bond. - **Alkanes** are saturated hydrocarbons and contain no functional groups. Each carbon atom is sp³ hybridised and has a tetrahedral molecular geometry. The names of alkanes always end with "ane". Examples include: - Methane, CH4 - Propane, CH3CH2CH3 - **Alkenes** are unsaturated hydrocarbons that contain the C=C functional group. The carbon atoms participating in the double bond are sp² hybridised and both have a trigonal planar molecular geometry. Alkene names end with "ene". Examples include: - Ethene, CH2CH2 - Propene, CH3CH=CH2 - **Alkynes** are unsaturated hydrocarbons that have the C≡C functional group. The carbon atoms participating in the double bond are sp hybridised, and both have a linear molecular geometry. Alkyne names end with "yne". Examples include: - Ethyne: CH≡CH - Propyne: CH3C≡CH - **Aromatic hydrocarbons** are unsaturated hydrocarbons that contain the benzene ring as a functional group. All carbon atoms in the ring are sp² hybridised, and all carbon atoms within the ring lie in the same plane. Note that there are two resonance structures for the benzene ring, and the actual benzene ring is a resonance hybrid. - Examples include - Benzene, C6H6 - Methylbenzene, C6H5CH3 ### b) Alkyl halides/alkenyl halides/aryl halides These are compounds in which a halogen atom replaces a hydrogen atom in a hydrocarbon. - In an alkyl halide, the halogen replaces an H on an sp³ hybridised carbon. Alkyl halides can be classified as primary, secondary or tertiary according to the number of carbon atoms bonded to the carbon bearing the halogen. - **Primary alkyl halide (1°)** - CH3CH2CH2-Cl: - **Secondary alkyl halide (2°)** - CH3CH2-CH-CH3 - **Tertiary alkyl halide (3°)** - CH3-C(CH3)-Cl - If the halogen is bonded to an sp² hybridised carbon in an alkene, the compound is termed an alkenyl halide. Compounds with a halogen bonded to a carbon within a benzene ring are termed aryl halides. Examples include: ### c) Alcohols and phenols An alcohol is an organic compound containing the following functional group: - One can view alcohols as derivatives of water where one of the hydrogen atoms is replaced with a group derived from an alkane, known as an alkyl group, often symbolised as R. As in water, the oxygen is sp³ hybridised and has a bent molecular geometry. - As with alkyl halides, alcohols are classified as primary, secondary and tertiary, as shown in the following examples: - **Primary (1°)** - CH3CH2CH2-OH - **Secondary (2°)** - CH3CH2-CH-CH3 - **Tertiary (3°)** - (CH3)3C-OH - Phenols are organic compounds in which the hydroxyl group is attached directly to a benzene ring. Phenols and alcohols have different chemical properties. ### d) Ethers Ethers are organic compounds consisting of two alkyl groups (denoted R, R' and consisting of an alkane with a hydrogen atom removed) attached to an oxygen atom. The oxygen atom is sp³ hybridised with a bent molecular geometry. - **Example** - H3C-O-CH2CH3 ### e) Amines - Amines are organic derivatives of ammonia where one or more nitrogen atoms have been replaced with an organic group R. Amines are classified as primary (one ammonia H replaced with organic group), secondary (two ammonia H replaced with organic group) and tertiary (three ammonia H replaced with organic group). As in ammonia, the N atom is sp³ hybridised with a trigonal pyramidal molecular geometry. - **Primary (1°)** - replace one H with R - **Secondary (2°)** - replace two H with R - **Tertiary (3°)** - replace three H with R ### f) Aldehydes and ketones Aldehydes and ketones both have the carbonyl group C=O where the carbon atom is sp² hybridised. In an aldehyde, the C in the carbonyl group is attached to two hydrogen atoms or to one carbon atom and one hydrogen atom. - **Formaldehyde** - H - **Acetaldehyde** - CH3-CHO In a ketone, the C in the carbonyl group is attached to two carbon atoms. - **Acetone** - CH3-CO-CH3 The carbonyl carbon atom in both cases has a trigonal planar molecular geometry. ### g) Carboxylic acids Carboxylic acids contain the carboxyl functional group: - **Acetic acid** - CH3-COOH ### h) Esters Esters are carboxylic acid derivatives in which the hydrogen in the carboxyl group is replaced with some organic group R. - **Example** - **Ethyl acetate** - CH3COOCH2CH3 ### i) Amides An amide is a carboxylic acid derivative in which the OH group within the carboxyl group is replaced with an NRR' group where R and R' could represent H or an organic group. - **Example** - CH3-C(=O)-NH2 On your own time, attempt problems 2.19, 2.29, 2.30, 2.31, 2.33, 2.34