Organic compounds are the building blocks of life, featuring various functional groups that give them unique properties. From alkenes with double bonds to carbonyl-containing structures, each group has its own reactivity and behavior in chemical reactions.

These functional groups define how organic molecules interact, influencing everything from drug design to material science. Understanding their structure and reactivity is key to mastering organic chemistry and unlocking the potential of carbon-based compounds in countless applications.

Functional Groups in Organic Compounds

Key functional groups in organics

• Alkenes ($C=C$) contain a double bond between two carbon atoms enables them to undergo addition reactions with electrophiles (ethene, propene, butene)
• Alkynes ($C≡C$) contain a triple bond between two carbon atoms makes them highly reactive and prone to addition reactions (ethyne (acetylene), propyne, butyne)
• Arenes are aromatic compounds containing benzene rings characterized by delocalized π electrons that make them stable but reactive towards electrophilic aromatic substitution (benzene, toluene, naphthalene)
• Carbonyl-containing structures feature a carbonyl group ($C=O$) that influences their reactivity
  • Aldehydes ($RCHO$) have the carbonyl group at the end of a carbon chain making them susceptible to nucleophilic addition reactions (formaldehyde, acetaldehyde, benzaldehyde)
  • Ketones ($RCOR'$) have the carbonyl group within a carbon chain and also undergo nucleophilic addition reactions (acetone, butanone, cyclohexanone)
  • Carboxylic acids ($RCOOH$) have a carbonyl group with a hydroxyl group ($OH$) attached giving them acidic properties and the ability to form esters and amides (acetic acid, benzoic acid, stearic acid)
  • Esters ($RCOOR'$) have a carbonyl group with an alkoxy group ($OR'$) attached making them prone to hydrolysis reactions (ethyl acetate, methyl benzoate, propyl butanoate)
  • Amides ($RCONH_2$, $RCONHR'$, $RCONR'R''$) have a carbonyl group with a nitrogen atom attached and can be primary, secondary, or tertiary (acetamide, N-methylacetamide, N,N-dimethylacetamide)

Influence of functional groups on reactivity

• Alkenes and alkynes undergo addition reactions due to the presence of π bonds
  • React with electrophiles like halogens, hydrogen halides, and water
  • Participate in hydrogenation and halogenation reactions that add atoms across the multiple bonds
• Arenes undergo electrophilic aromatic substitution reactions because the delocalized π electron system makes them reactive towards electrophiles
  • Examples include halogenation, nitration, sulfonation, Friedel-Crafts alkylation and acylation which substitute hydrogen atoms on the benzene ring
• Carbonyl-containing structures have distinct reactivities based on their specific functional groups
  • Aldehydes and ketones undergo nucleophilic addition reactions at the carbonyl carbon with Grignard reagents, hydrides, and amines and participate in condensation reactions (aldol condensation, Claisen condensation)
  • Carboxylic acids have acidic properties due to the hydroxyl group, undergo esterification reactions with alcohols, and form amides when reacted with amines
  • Esters are susceptible to hydrolysis reactions that yield carboxylic acids and alcohols and participate in transesterification reactions
  • Amides are relatively stable compared to other carbonyl compounds but can undergo hydrolysis under acidic or basic conditions
• The polarity of functional groups affects their reactivity and solubility in different solvents

Classification of organic compound families

• Alkenes: $C_nH_{2n}$
  • Named using the suffix "-ene" to indicate the presence of a double bond
  • Example: $CH_2=CH_2$ is ethene, the simplest alkene
• Alkynes: $C_nH_{2n-2}$
  • Named using the suffix "-yne" to denote the presence of a triple bond
  • Example: $CH≡CH$ is ethyne, also known as acetylene
• Arenes: contain one or more benzene rings
  • Named as derivatives of benzene by indicating substituents
  • Example: $C_6H_5CH_3$ is toluene, a common aromatic solvent
• Aldehydes: $C_nH_{2n}O$
  • Named using the suffix "-al" to signify the terminal carbonyl group
  • Example: $CH_3CHO$ is ethanal, the simplest aldehyde
• Ketones: $C_nH_{2n}O$
  • Named using the suffix "-one" to indicate the internal carbonyl group
  • Example: $CH_3COCH_3$ is propanone, commonly known as acetone
• Carboxylic acids: $C_nH_{2n}O_2$
  • Named using the suffix "-oic acid" to represent the carboxyl group
  • Example: $CH_3COOH$ is ethanoic acid, also called acetic acid
• Esters: $C_nH_{2n}O_2$
  • Named using the alkyl group and the carboxylate anion
  • Example: $CH_3COOC_2H_5$ is ethyl ethanoate, a fruity-smelling ester
• Amides: $C_nH_{2n+1}ON$
  • Named using the suffix "-amide" to denote the carbonyl-nitrogen group
  • Example: $CH_3CONH_2$ is ethanamide, the simplest amide

Structural considerations in organic compounds

• Functional groups: specific atoms or groups of atoms within molecules that determine the characteristic chemical reactions of those molecules
• Isomerism: the existence of molecules with the same molecular formula but different structural arrangements, which can affect their properties and reactivity
• Hybridization: the mixing of atomic orbitals to form new hybrid orbitals, which influences molecular geometry and bonding in organic compounds