Organic Chemistry: Some Basic Principles and Techniques short notes

Naming and isomerism

• Pick the longest chain with the main functional group, and give it the lowest number.
• Structural isomers include chain, position, functional group and metamerism types.
• Stereoisomers include geometrical and optical types.

Electron effects

• Inductive effect: shifting of σ electrons along a chain, which weakens with distance.
• Resonance: delocalisation of π electrons or lone pairs, which stabilises a molecule.
• Electromeric effect: a temporary shift caused by an attacking reagent.
• Hyperconjugation: delocalisation of σ electrons from C-H bonds next to a carbocation or double bond.

Intermediates

• Carbocation: sp², planar. Stability is 3° > 2° > 1° > methyl.
• Carbanion: usually sp³. Stability is methyl > 1° > 2° > 3°.
• Free radical: stability is 3° > 2° > 1° > methyl.
• Nucleophiles are electron-rich, and electrophiles electron-poor.

Purification and analysis

• Crystallisation, distillation, sublimation, differential extraction and chromatography separate compounds.
• Lassaigne's test detects N, S and halogens.
• Dumas and Kjeldahl methods estimate nitrogen, though Kjeldahl doesn't work with nitro or azo groups, or pyridine.

Estimation formulas

Carbon

$\displaystyle \%\text{C} = \frac{12\times m_{\text{CO}_2}\times100}{44\times m}$

Hydrogen

$\displaystyle \%\text{H} = \frac{2\times m_{\text{H}_2\text{O}}\times100}{18\times m}$

Nitrogen (Kjeldahl)

$\displaystyle \%\text{N} = \frac{1.4\times N\times V}{m}$

N is the acid's normality, and V the acid used in mL.