The chemistry of carbon - functional groups, reaction mechanisms, nomenclature, and stereochemistry.
Organic chemistry is organized around functional groups - specific arrangements of atoms that determine a molecule's chemical behavior. The carbon backbone is relatively inert; it's the functional groups that make chemistry happen.
The systematic naming system: (1) Find the longest carbon chain (parent name), (2) Number from the end nearest the first substituent, (3) Name and number substituents as prefixes, (4) Add suffix for the main functional group (-ol, -al, -one, -oic acid).
Longest chain: 4 carbons → butane. OH group on carbon 2 → suffix -ol. Number from the end nearest the OH.
Nucleophilic substitution is one of the most important reaction types. The mechanism depends on the substrate structure, nucleophile strength, and solvent.
One step: nucleophile attacks as leaving group departs. Backside attack → inversion of stereochemistry. Favored by: strong nucleophile, primary substrate, polar aprotic solvent. Rate = k[substrate][nucleophile].
Two steps: (1) Leaving group departs → carbocation, (2) Nucleophile attacks. Racemization (mix of R and S). Favored by: weak nucleophile, tertiary substrate, polar protic solvent. Rate = k[substrate].
(a) CH₃Br: primary substrate + strong nucleophile (OH⁻) → SN2. Clean backside attack, inversion.
(b) (CH₃)₃CBr: tertiary substrate + weak nucleophile (H₂O) → SN1. Stable 3° carbocation forms first, then water attacks from either side → racemization.
A carbon bonded to four different groups is a chiral center (stereocenter). Chiral molecules exist as non-superimposable mirror images called enantiomers (R and S configurations). They rotate plane-polarized light in opposite directions.
The C=C double bond in alkenes is electron-rich, making alkenes nucleophilic. They undergo addition reactions where the π bond breaks and two new σ bonds form.
The C=O carbonyl group is polar - carbon is electrophilic (δ+) and oxygen is nucleophilic (δ−). Nucleophiles attack the carbon, making carbonyl compounds incredibly versatile in synthesis.
NaBH₄ or LiAlH₄ reduce C=O to C-OH. Grignard reagents (RMgBr) add carbon chains. HCN adds to form cyanohydrins.
Two carbonyl molecules combine: one acts as nucleophile (enolate), one as electrophile. Forms new C-C bond - essential for building complex molecules.