Question

can questions 7.74 A and B be answered please and question 7.75. numbered questions please

7.74 (9)-1-Bromo-1,2-diphenylethane reacts with a strong base to produce cis-stilbene and trans-stilbene: Br NaOET cis-Stilbene trans-Stilbene (major product) (a) This reaction is stereoselective, and the major product is trans- stilbene. Explain why the trans isomer is the predominant product. To do so, draw the Newman projections that lead to formation of each product and compare their stability. (b) When (R)-1-bromo-1,2-diphenylethane is used as the starting sub- strate, the stereochemical outcome does not change. That is, trans- stilbene is still the major product. Explain. 7.75 There are two stereoisomers of 1-tert-butyl-4-chloro-cyclohexane. One of these isomers reacts with sodium ethoxide in an E2 reaction that is 500 times faster than the reaction of the other isomer. Identify the isomer that reacts faster, and explain the difference in rate for these two isomers.

Answer 1

7.74 (a) In this question Nao Et is acting as a base so it is just a case of £2 ellimination and E2 ellimination always goes through trans five membered transition state. So trans ellimination in favour own cis elimination in Neroman projection, (S)-l-Bromo -1, 2-diphenylethane If we draw the above molecul we will get - Phol metro Br HT c-c slogle H bondion eń (I) Ph bond rotation (S)-1-Bromo-1,2-diphenylethane c-c single bond rotation AB Both (I) and (II) we will get by just a rotation. of c-c single bood. Both (I) and (I) are same molecule. Even (S)-1-Bromo -1,2-diphenylethane (I) (11) are same molecule . u 1 ph BRSH Ph pw H Ph it t obt Trans-five membered Transition state Trans-stilben

BV 14 & PW Ph SVGA-ort HP ---067 cis-five membered Transition state a in cis-stilbene As trans-stilbene we are getting from trans ellimination. So, trass-Stilbere is the major product. Because we know that for 12 ellimisation we always getting major product from trans ellimination not from cis- ellimination. 7.74 (6) a Br V (R)-1-bromo-1,2-diphenylethane TAYO

7.74 (6) (R)-1-bromo-1,2-diphenylethane If we draw the above molecule in Newman projection. Then we will get Br ph Br / bond Rotation Ph. I 'C-Csiogh t Ic-c single bood rotation Bran Ph It ph) Anti-ellissiration , Phụ tr trans-stilbere Congor product . Ph Tort, eis-elliminatimph cis-stilbere Coninor product