Question

6. Which of the following carbocations would NOT be likely to undergo rearrangement? A) CH3CHCHCH3 CH3 CH3 B) CH3CHOCH3 CH3 CH C) CH3CCH2 CH3 D) CH3 CH3CHCH2 E) CH3 CH3CCHCH2CH3 CH3 7. Which alcohol would initially produce the most stable carbocation when treated with concentrated H2SO4? A) CH3 CH3CCH2 CH3 он CH3 B) CH3CHCHCH3 он CH3 C) CH3CHCH2CH2OH CH3 D) HOCH2 CHCH2CH3 E) CH2 OH CH3CHCH2CH3 Page 4

Answer 1

The stability of carbocations increases as we go from primary to secondary to tertiary carbons due to the +I effect and hyperconjugation. If formed carbocation is less stable then it will try to achieve the stability by undergoing rearrangement. But if carbocation is already stable enough like tertiary carbocation then such carbocation will not show rearrangement. the details of these problems are shown below-

Hydnde shift CH3 CHO 3-carbocation tmost stable] 2-Car bocodion CHA Meth CHO G) とH3 CH 2-carbocoion 39carbocation More stable CH2 Hydide CH3-c-CH-CH 2carboca less stable] Already 3-carbocation CMove stabl1 CH3 CHO 4,2- Hydide CH3- cH 2 3- carbocotion more stablej CHO 1,2-meth sft CH0 > CHg-C-CH-CH2 -CH3 3- CH- CH2-CHO CHO CHS [More stable.] Зе.carbocodon 2 carbocation Thus the covect answer is option C CHO conc. H2SCL -cabacoion mast stablk] CHS conc. H2S0 CC-CH CH4 он 29, carbocation [stable] CH2 Conc. H2S04 carbocoion tess stable]

CHO CH3 DJ Ho-CH2-ch-CH2-CHg conc.ngs → CH2 12 carbecoion Eless stable CH2-OH Conc H2so4 19 carbocafion Cless stoble Thus the corect ansuer is option A