Which of the following carbocations is likely to rearrange? A) I B) II C) III D)

Question

Which of the following carbocations is likely to rearrange? A) I B) II C) III D) IV E) II and IV What reagents are needed to accomplish the following transformation? A) H_2O/H^+ B) H_2O/Peroxide C) OH^- D) BH_3 E) 1. BH_3, 2. HO^-, H_2O_2 What reagents can best be used to accomplish the following transformation? A) 1. BH_3-THF 2. HO^-, H_2O_2 B) H^+, H_2O C) 1. Hg(OAc)_2, H_2/THF 2. NaBH_4 D) 1. Hg(O_2CCF_3)_2, CH_3OH 2. NaBH_4 E) NaOH, H_2O Upon hydrogenation, which of the following alkenes releases the least heat per mole? A) 3, 4-dimethyl-1-hexene B) (Z)-3, 4-dimethyl-2-hexene C) (E)-3, 4-dimethyl-2-hexene D) (Z)-3, 4-dimethyl-3-hexene E) (E) -3, 4-dimethyl-3-hexene Which of the following are the elimination products of the reaction shown below? CH_3CH_2Br + -OH rightarrow A) CH_3CH_2Br + H + O- B) HOCH_2CH_2Br C) CH_3CH_2OH + Br- D) CH_2=CH_2 + Br- + H2O E) CH_2=CHBr + H2O What is the major organic product of the following reaction? A) 2, 3-dimethyl-1-hexene B) 2, 3-dimethyl-2-hexene C) 2-isopropyl-1-pentene D) (Z) -2, 3-dimethyl-3-hexene E) (E)-2, 3-dimethyl-3-hexene Which of the following alkyl halides forms the most stable carbocation when it undergoes an El reaction? A) I B) II C) III D) IV C) V

Explanation / Answer

Ans:

55 = E (Stability of C+ 30 > 20 > 10)

56 = E (Hydroboration oxidation reaction, giving anti-markonikov porduct)

57 = A (Hydroboration oxidation reaction, giving anti-markonikov porduct)

58 = D (tetrasubstituted C=C is the most stable and hence releases the least heat during the reaction. Stability of C=C is as: tetra > tri > di > mono substituted alkenes- following zaitsev rule)

59 = D (eleimination reaction, abastracts beta H next to C attached to halogen)

60 = D (big bulky base is used, so it will abstract the H which is least hindered)

61 = D (allylic C+ is the most stable and also when formed is stabilized by the C=C in vicinity)

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