JEE Chemistry Organic Chemistry Notes Set 01

Naming and Stereochemistry

1. Amide has higher priority than ketone in naming, and the CIP rules decide E and Z. Compare the first point of difference, atom by atom, in decreasing atomic number.
2. A molecule is optically active if it has no plane or centre of symmetry. Cumulated dienes (C=C=C) with two different groups at each end and hindered biphenyls are chiral without a stereocentre.
3. Only sp2 carbons: every carbon must carry a double bond or lie in an aromatic ring.

Acidity and Resonance

1. Acidity of nitrophenols: para (pKa about 7.1) > ortho (7.2) > meta (8.4) > phenol (10). Ortho is slightly weaker because of intramolecular hydrogen bonding.
2. Resonance needs conjugation. An sp3 carbon between the lone pair or double bond and the pi system breaks it.

Reactions

1. HBr adds to an alkene through the more stable carbocation, so a benzylic cation is preferred.
2. Side chain oxidation: toluene gives benzoic acid with KMnO4, and soda lime decarboxylation gives benzene.
3. Diazonium salts from primary aromatic amines (NaNO2/HCl, 0-5 degrees Celsius) are converted by CuCN/KCN to nitriles (Sandmeyer).
4. An N-aryl amide is nitrated on the N-aryl ring, mainly para.
5. Good nucleophile and good leaving group order among halides: I- > Br- > Cl-.
6. Aldehydes are oxidised by Tollens', Fehling's and Schiff's reagents, ketones are not. Grignard adds to both.
7. Glucose with Na/Hg gives sorbitol, with Br2 water gluconic acid and with HNO3 saccharic acid.
8. Saccharin is the cyclic imide of 2-sulphobenzoic acid, about 550 times sweeter than sucrose.