Isomers: branching and the para effectसमावयवी: शाखन और पैरा प्रभावIsomers: branching and the para effect

Class 12 Chemistry · Chapter 6 · interactive diagram

Parts and what they mean

• 1-Bromobutane (straight chain), b.p. 375 K (1-ब्रोमोब्यूटेन (सीधी शृंखला), क्वथनांक 375 K) — Largest surface contact → highest b.p. of the three isomers (NCERT values).
• 2-Bromobutane, b.p. 364 K (2-ब्रोमोब्यूटेन, क्वथनांक 364 K) — One branch point → lower b.p.
• 2-Bromo-2-methylpropane, b.p. 346 K (2-ब्रोमो-2-मेथिलप्रोपेन, क्वथनांक 346 K) — Most branched → lowest b.p. of the three (NCERT).
• Why branching lowers b.p. (शाखन से क्वथनांक क्यों घटता है) — A branched molecule is more compact (nearly spherical), so the area of contact and the van der Waals forces between molecules are smaller.
• o-Dichlorobenzene (1,2-) (o-डाइक्लोरोबेन्ज़ीन (1,2-)) — b.p. 453 K, m.p. 256 K (NCERT).
• m-Dichlorobenzene (1,3-) (m-डाइक्लोरोबेन्ज़ीन (1,3-)) — b.p. 446 K, m.p. 249 K (NCERT).
• p-Dichlorobenzene (1,4-) (p-डाइक्लोरोबेन्ज़ीन (1,4-)) — b.p. 448 K but m.p. 323 K — much higher, because the symmetrical para isomer fits better in the crystal lattice.

Original diagram drawn by Simple Learning Hub, based on the NCERT textbook. Report a mistake