NEET Chemistry NCERT Reactions & Trends
1. Organic Chemistry Named Reactions
Must-Know Carbonyl & Amine Reactions
- Aldol Condensation: Aldehydes/ketones with $\alpha$-H in presence of dilute alkali form $\beta$-hydroxy aldehydes (aldols) which upon heating dehydrate to $\alpha,\beta$-unsaturated carbonyls.
- Cannizzaro Reaction: Aldehydes lacking $\alpha$-H (e.g. $\text{HCHO}$, $\text{C}_6\text{H}_5\text{CHO}$) in $50\%\text{ NaOH}$ disproportionate to alcohol and carboxylate salt.
- Hoffmann Bromamide Degradation: $1^\circ$ amide $+ \text{Br}_2 + 4\text{KOH} \xrightarrow{\Delta} 1^\circ\text{ amine} + \text{K}_2\text{CO}_3 + 2\text{KBr} + 2\text{H}_2\text{O}$.
- Reimer-Tiemann Reaction: Phenol $+ \text{CHCl}_3 + 3\text{NaOH} \to$ Salicylaldehyde (intermediate dichlorocarbene $:$$\text{CCl}_2$).
2. Coordination Chemistry & Periodic Trends
Crystal Field Splitting & Lanthanoid Contraction
- Octahedral Splitting: $d$-orbitals split into lower $t_{2g}$ ($d_{xy}, d_{yz}, d_{zx}$) and higher $e_g$ ($d_{x^2-y^2}, d_{z^2}$). $\Delta_o$ energy gap.
- Spectrochemical Series: $\text{I}^- < \text{Br}^- < \text{Cl}^- < \text{F}^- < \text{OH}^- < \text{H}_2\text{O} < \text{NH}_3 < \text{en} < \text{CN}^- < \text{CO}$.
- Lanthanoid Contraction: Poor shielding by $4f$ electrons leads to steady decrease in atomic/ionic radii. Causes identical radii in $\text{Zr} / \text{Hf}$, $\text{Nb} / \text{Ta}$, $\text{Mo} / \text{W}$.