E1 Reaction and Related Reactions © Subjective Questions Direction (Q. Nos. 1-5) These questions are subjective in nature, need to be solved completely on notebook. 11 Propose a mechanism for the formation of these products in the solvolysis of this alkyl bromide. sun oecn x4 +C i ed NZ 2. Consider the following statements in reference to Sy1, Sy2, E1, and E2 reactions of haloalkanes. To which mechanism(s), if any, does each statement apply? i. Involves a carbocation intermediate Is first order in haloalkane and first order in nucleophile |. Involves inversion of configuration at the site of substitution /. Involves retention of configuration at the site of substitution /. Substitution at a chiral center gives predominantly a racemic product |. Is first order in haloalkane and zero order in base Is first order in haloalkane and first order in base vii. 1s greatly accelerated in protic solvents of increasing polarity ix. Rearrangements are common x. Order of reactivity is 3° > 2° > 1° xi. Order of reactivity is methyl > 1° > 2° > 3° 3 Predict the major elimination product in the following reaction. CH, OH Seep ac Aaet, CH, Br Propose mechanism and derive rate law of the above reaction. Also draw appropriate activation energy diagram. 4 How the following factors affect the reactivity in an E1 reaction? i i. Structure of substrate ii, Solvents iii, Lewis acid lv. Strength of base 5 Consider the following two substrate and compare their reactivity in E1 reaction when cate in ethanol. CoH CaHkOH | i Us —C—co— pe a Coy ( i CH; ———> by Scanned with CamScanner@ Only One Option Correct Type Direction (2. Nos. 6-13) This section contains 8 mutiple choice questions. Each quastion has four isis (8). (0). (0) and (0), out of which ONLY ONE option is corect. 6 The incorrect statement concerning E1 reaction is ‘a. polar protic solvent increases reactivity b. lewis acid catalyses reaction ¢. reaction proceeds via carbocation intermediates d, reaction proceeds via a single transition state 7, The correct statement regarding a unimolecular elimination reaction is a. Rearrangement of carbon skeleton may occur during elimination reaction b. Reaction is stereospecific «¢, If *C replaces a-carbon of substrate, reactivity remains unaltered 4d. Inthe given condition of E1 reaction, no substitution reaction takes place 8 Consider the following reaction, CH, CH, CHy | GthOH, I I HEF CHa CH SHOH, 4. C= CH-CH, + H,C=C—CHa—CHs ee L 1 Br ‘The correct statement conceming | and I! is a. Lis the major product as itis formed at faster rate than I! ». Ilis the major product as it is formed at faster rate than | c. Lis major product as itis more stable than I! 4. Land Il are formed in comparable amounts 9 Consider the following elimination reaction, H__ CHy H__ CH, CHs — xf (CH) H (CHy,cH HH H | vero oir a | When reaction is carried out with C,HONain ethanol, 2-menthene is the major product while 3-menthene is the major product if reaction is substrate is heated in ethanol only. Itis due to ‘a. with strong base, less substituted alkene is always the major product. ». with strong base, reaction proceeds by E2 mechanism while with weak base, E1 reaction takes place. c. methyl group gives steric hindrance to strong base in E2 reaction. 4d. isopropyl group gives steric hindrance to strong base in E2 reaction. 10. The reaction of tertiary butyl chloride in water to yield tertiary buty! alcohol is not appreciably affected by dissolved NaF; in DMSO, however, NaF bring about rapid formation of isobutene. It is because of 2, in DMSO, E1 reaction predominates over Sy1 b. E2 reaction is preferred over Sy1in DMSO ©. E2 reaction is preferred over Sy2in DMSO 4. fluoride ion is not solvated by DMSO 11 When (CH, ),C—Clis heated in ethanol, both alkene and ether are formed | simultaneously by E1 and Sy reaction. Which of the following will have adverse effect on both of the above reaction? 2. Presence of Lewis acid b. Presence of some water in ethanol ©. Presence of some NaCl d. Presence of some CHCl, Scanned with CamScanner12. Consider the following reaction, CH, ie ie nc——otcr cee HE GHG 4 HCC b oy CHO CH, CH Sy 1 Increasing temperature increases the proportion of elimination (E1) product because @. Et productis enthalpy favoured ——_b. 1 product is entropy favoured ©. Sy "product is entropy favoured d. Sytproduct is enthalpy favoured 13. Which isthe least reactive halide in both E1 and Sy 1reaction? cl —- b ° a 4. a q Br cl © One or More than One Options Correct Type Direction (0. Nos. 14-16) This section contains 3 mutiple choice questions. Each question hes four hoices (8), (2), (c) and (6), out of which ONE or MORE THAN ONE are corrct. 14 Consider the following reaction, CH;CH, He io, +0,H,0H “SS, a eotope ‘The possible alkene(s) is/are CH, CH, CH, CH, a. H.C=C—CH—CH, b. H,C—C=C—cH, CH; CH, CH, c. He oie, d. H—CH—'C=cH, CH, 15 Consider the following elimination reaction, CHsOH Heat The possible elimination product(s) se The correct statement regarding an E1 reaction is/are ? 1a. Reaction rate is same for deuterated and un-deuterated halides b. R—Cland R—OTs reacts at same rate (—OTs = tosylate) c. RI” is more reactive than R—1"" d. Stronger base increases the reactivity 16 Scanned with CamScannerComprehension Type Direction (0. Nos. 17-19) This section contains a peragraph, describing theory. experiments, d Three questions related tothe paragraph have been given. Each question has only one correct ‘among the four given options (a), (2). (c) and (o. Passage Consider the following reaction. The tertiary butyl group can be cis or trans to tosylate group. Answer the following questions based on the knowledge of E2 and E1 reaction mechanism. O° HgC, I NaOCeH ~ o-s CHs ———— HyC— i CH,0H Hy” O° x 47 The correct statement concerning above elimination reaction is ‘a. when tertiary butyl group is trans, reaction occurs rapidly and deuterium is lost from B-carbon b. when tertiary butyl group is trans, reaction occurs rapidly and hydrogen is lost from | B-carbon . when tertiary butyl group is cis, reaction occurs rapidly and deuterium is lost from B-carbon 4. when tertiary butyl group is cis, reaction occurs rapidly and hydrogen is lost from Bcarbon 18 When tertiary butyl group and tosylate group are trans, the correct statement is 1. reaction occurs slowly and hydrogen is lost from B-carbon ». reaction occurs slowly and both hydrogen and deuterium are lost from B-carbon . reaction occurs rapidly and hydrogen is lost from B-carbon 4d. reaction occurs rapidly and deuterium is lost from B-carbon 419 Ifthe rate of reaction is independent of NaOEt concentration, it is concluded that a. tertiary butyl group is cis to tosylate b. tertiary butyl group is trans to tosylate c. substitution reaction occur predominantly d. NaOEt is in large excess © One Integer Value Correct Type Direction (2. Nos. 20 and 21) This section contains 2 quastions. When worked out wil result in an ‘integer from 010 8 (both inclusive). 20 Consider the following reaction, | CHs catgon Oe Toot a In principle, how many different alkenes are possible by the above elimination reaction? 21 E1 reaction always competes with ‘Sy treaction. How many Sy1 products are formed in principle in the question number 207 Scanned with CamScannerDPP.9 E1 Reaction and Related Reactions Gu—cry as x ‘Oca st e 2.) Bah S1 and E! reaction mechanism imave carbocation reece tomedas. (2 reaction is rst order wih respect to each ay halide and mcteophie. ( BotnS,2 and, reactons ime inversion of configuration cecarbons. However there occur complete inversion in $2 {Walden's inversion) whereas partial racemisation and net iverson in Section (6 In 1 reacton racerisation takes place which occur by equal axrounts of version and retention at chiral a-carbon ( S41 reaction proceeds by predominant recemisation of configuration but nt inversion. (9 Et reaction ati rectly proporionalto concentration af aly had but independent of base concentration. Re, = KI ~ x) (8) 2 reaction is second order overal, est-ordar in ay hae and frst order in base concentration (vi) Both S\1.and Et reactions are accelrated by protic stents fhe war, acohol, (6 Reaangerenis of carbocation intermediates very common inbot Sand £1 reaction. (6) This is the order of reactivity In E2. 1 and 1 reactions. (8) Tiss the order of react n 2 reaction i CHs 3. 9c —to, ond ort oy & oH, MOM 0, —G—chcHy Hs © the ot a 7 oy aye a |.) In Et reacton, carbocation inernedite 4 OF vy ol al hades > > F ONE Heng &) Por proc sovents tke water, alcool ete 2 reaction as they stabilises carbocation, sect & (i) Lowis acids act as cats 28 they hep in he carbocation tormaten R—Ol+ AC, —+ RY + AICS wR (4 Strength of base has no 08m E1 reaction boca ba imvehed in fast, nonate determining stop, . 6. Both reactions () and (i) occur al same rate because Cy, ‘C—Dbonds wil be broken in fast, nonate determing sgn 6. (6 E1 Reactors invoWe carbocation intermediates wig Grracorstes of rearrangement rio more sabe cays fence involves more tan One anstion sales (usualy, h w i t Pt ey dagen re Sfanpica et nace Tittle vara tn aga reacion 7. (2) E1 reaction proceeds via carbocation intermediate, rearrangement of carbon skeleton is. very common in fe reacton 8. (¢ Tisisan example ot Et reaction and more substiuted kere (his tormed asthe malor product. 9. (0) With strong base CzHsONa, reaction proceeds by E2 ‘mechanism Since, there is fo Hin the anf poston at tray Bcarbon, deprotonation occur from secondary -carbon gn) ‘2-menthene as the major product. On the other hand, with week base, reaction proceads by E1 mechanism and the most sabe terbary carbocation formed, ges the mejor product 3 methane 10. () Polar aprotic solvents DMSO strongly favour E2 reaction ‘ving isobutone product. 11. (c) Both $,1 and E1 reaction involve formation of carbocation intermedi in iow rate determining stop as oH sow Giye—a = oer sor cH Presence o! NaC! derive the above reaction in backwar recon ‘by Le-Chatelier’s principle, hence has adverse effect on both Et and reaction, oe 12,0) DOG —FH—chhy + CaHOH S44 CHy Hy OH -— CH— CH, +O OH, CHy CH, cy md-pnos 4, one ie +o Faction (i) leads to greater increase in entropy (An = 1) Here®. {evoured at higher temperature due to greater decrease n 4G ‘han for reaction ( Scanned with CamScanner13. (c) Carbocation at bridge head carbon ot bicyctic hgh unstable due to lack of plana para +14, (ab) Reaction proceeds by E1 mechanism see CHy oH cH, = a ob _thon, I a 0 CHy CH, | cr,—du— —CH, both are 3 » CHs CH, CHsCHs +, Lt ° 0) 5 chy C—CH—CH, + CH —C=G—CHy a ¢ © Cy CHy cHicHy =, on, dnt i 9 5 cH, CHC CH, + CH) —C-=G—CH, a) o 16. (a,b,¢) Reaction proceeds by E1 mechanism. ay nar @) ) @ 18. (ac) in E1 reaction, carbocation intermediate “undergo ‘eprotonation inthe fast, non-rate determining step, henceC—H 8nd C—D bonds react at same rate. However, C—X bond is broken in fst, slow, non-rate determining step, hance A—I'” "Pacts at faster rate than A—1"" 17. (d) The reaction involves E2 elimination mechanism in which base ‘approaches to B-H from side anti to leaving halide in the rate ‘determining step. Hence, if tertiary butyl group isis to tosytate, it ‘would not give steric hindrance to the base approaching from ‘opposite side to -H. 48. (b) When tertiary butyl group istrans to tosylate, E2 reaction willbe dificult and E1 reaction would be preferred. Since, €1 reaction ‘occur slowly and hydrogen is lostin fast step, both Hand D willbe lost with equal ease 19. (b) When tertiary buty! group istrans to leaving hale, €2 reaction will be highly sterically hindered and £1 reaction would be preferred. 20. (@) Total 8 akenes Oe =e 0 Scanned with CamScanner