Question

Can you explain the answers?

1. Which of the following molecules should have the longest max? он о 2. Which of the following has the lowest heat of hydrogenation?

Answer 1

орн hinders hinders Longligation o pH fully conjugated system (no hinderance A longest & max Conjugation (Sp-c) Hinderance in complete conjugation ③) Aromatic System (highly stable) Non- aromatic (comparatively less stable than B o ot have higher heat of hydrogenation than B,

1. We know higher the conjugation, more will be the Lambda maximum.

Since A fully conjugated having all carbon SP2 hybridized. so, a complete conjugated system exists. therefore it has longest wavelength

on the contrary, other compounds have SP3 carbon which is hindering complete conjugation system. therefore, they have comparatively lower value of Lambda Max.

2. We know more stable the system lower will be heat of hydrogenation. heat of hydrogenation is defined as the amount of energy released when 1 mole of hydrogen gets added across the system.

B is highly stable due to aromaticity. therefore, it will have least heat of hydrogenation while rest of the compounds are not as stable as B due to absence of aromaticity. So, they will have comparatively higher heats of hydrogenation.