Organic Chemistry: Alkanes, Alkenes, and Alkynes

• Organic chemistry studies the structure, properties, composition, reactions, and preparation of carbon-containing compounds.
• These compounds can contain hydrogen, nitrogen, oxygen, halogens, phosphorus, silicon, and sulfur.
• Organic chemistry is a bridge between chemistry and life sciences.
• It underpins biochemistry, medicine, and materials science.
• Carbon's capacity to form stable chains and rings and bond with various elements results in a vast number of organic compounds.
• Organic compounds are classified by functional groups, which dictate a compound's characteristic chemical reactions.

Alkanes

• Alkanes are hydrocarbons containing only single bonds.
• They are saturated hydrocarbons.
• Alkanes have low reactivity due to stable C-C and C-H bonds.
• Combustion is a highly exothermic reaction of alkanes with oxygen, producing carbon dioxide and water.
• Halogenation is when a hydrogen atom in an alkane is replaced by a halogen atom.

Alkenes and Alkynes

• Alkenes contain at least one carbon-carbon double bond.
• Alkynes contain at least one carbon-carbon triple bond.
• They are unsaturated hydrocarbons.
• Alkenes and alkynes are more reactive than alkanes due to π bonds.
• Addition reactions occur where atoms or groups add across the multiple bond.
• Hydrogenation is the addition of hydrogen (H₂) across a double or triple bond.
• Halogenation is the addition of halogens (e.g., Cl₂, Br₂) across a double or triple bond.
• Hydration is the addition of water (H₂O) across a double or triple bond, often using an acid catalyst.

Alcohols and Ethers

• Alcohols have a hydroxyl group (-OH) bonded to a carbon atom.
• Alcohols form hydrogen bonds, leading to higher boiling points and increased water solubility compared to alkanes of similar molecular weight.
• Alcohols undergo dehydration to form alkenes, especially with an acid catalyst at high temperatures.
• Ethers contain an oxygen atom bonded to two alkyl or aryl groups (R-O-R').
• Ethers are relatively unreactive but can be cleaved under harsh conditions using strong acids.

Aldehydes and Ketones

• Aldehydes contain a carbonyl group (C=O) with at least one hydrogen atom attached to the carbonyl carbon.
• Ketones contain a carbonyl group (C=O) with two alkyl or aryl groups attached to the carbonyl carbon.
• Aldehydes are more reactive than ketones due to less steric hindrance around the carbonyl carbon.
• Both aldehydes and ketones undergo nucleophilic addition reactions at the carbonyl carbon.
• Aldehydes are easily oxidized to carboxylic acids, but ketones are more resistant to oxidation.

Carboxylic Acids and Esters

• Carboxylic acids contain a carboxyl group (-COOH), consisting of a carbonyl group and a hydroxyl group attached to the same carbon atom.
• Carboxylic acids are weak acids and donate a proton from the hydroxyl group.
• Esters are carboxylic acid derivatives where the hydroxyl group is replaced by an alkoxy group (-OR').
• Esterification is the reaction between a carboxylic acid and an alcohol, typically under acidic conditions, forming Esters
• Hydrolysis cleaves esters back into a carboxylic acid and an alcohol in the presence of water, acid, or base.

Amines and Amides

• Amines contain a nitrogen atom with one, two, or three alkyl or aryl groups attached.
• Amines are basic and accept a proton to form ammonium ions.
• Amides contain a nitrogen atom bonded to a carbonyl carbon.
• Amides are formed through a reaction between a carboxylic acid derivative and an amine.
• Amides are generally less reactive than esters due to resonance stabilization.

Stereochemistry

• Stereoisomers are molecules with the same molecular formula and connectivity but different spatial arrangements of atoms.
• Enantiomers are stereoisomers that are non-superimposable mirror images.
• A chiral center is a carbon atom bonded to four different groups.
• Diastereomers are stereoisomers that are not mirror images.
• Cis-trans isomers (geometric isomers) occur in alkenes and cyclic compounds where substituents are on the same side (cis) or opposite sides (trans) of the double bond or ring.

Reactions

• SN1 reactions are unimolecular nucleophilic substitution reactions which proceed through a carbocation intermediate.
• SN2 reactions are bimolecular nucleophilic substitution reactions occurring in one step with inversion of stereochemistry.
• E1 reactions are unimolecular elimination reactions that proceed through a carbocation intermediate and form alkenes.
• E2 reactions are bimolecular elimination reactions occurring in one step that require a strong base, and form alkenes.