21. Rank the aromaticities of the following compounds from most stable to least stable. (i) thiophene (ii) benzene (iii) pyrrole (iv) furan (A) ii ＞ i ＞ iii ＞ iv (B) ii ＞ iv ＞ iii ＞ i (C) ii ＞ iv ＞ i ＞ iii (D) ii ＞ iii ＞ iv ＞ i (E) iv ＞ ii ＞ i ＞ iii

22. Which of the following is true about the Witting reaction? (A) The formation of carbon-carbon double bond from carbonyl compounds (aldehydes and ketones) and triphenylphosphite is known as the Witting reaction. (B) The Horner-Wadsworth-Emmons reaction is a variation of the Witting reaction. The major is usually the (Z)-alkene isomer. (C) The Horner-Wadsworth-Emmons reaction involves use of a phosphonate ester instead of a triphenylphosphonium salt. (D) A cis oxaphosphetane intermediate is formed to produce a ( E )-alkene in the Wittig reaction. (E) All of these choices.

21. Rank the aromaticities of the following compounds from most stable to least stable. (i) thiophene (ii) benzene (iii) pyrrole (iv) furan
(A) ii ＞ i ＞ iii ＞ iv
(B) ii ＞ iv ＞ iii ＞ i
(C) ii ＞ iv ＞ i ＞ iii
(D) ii ＞ iii ＞ iv ＞ i
(E) iv ＞ ii ＞ i ＞ iii

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