Portmess Homework Q&S 119

Portmess Homework Q&S 119 - 5.38 The problem states...

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( h ) This example has been reported in the chemical literature, and in spite of the complexity of the starting material, elimination proceeds in the usual way. ( i ) Again, we have a fairly complicated substrate, but notice that it is well disposed toward E2 elimination of the axial bromine. ( j ) In the most stable conformation of this compound, chlorine occupies an axial site, and so it is ideally situated to undergo an E2 elimination reaction by way of an anti arrangement in the transition state. The minor product is the less highly substituted isomer, in which the double bond is exocyclic to the ring. 5.37 First identify the base as the amide ion (H 2 N 2 ) portion of potassium amide (KNH 2 ). Amide ion is a strong base and uses an unshared electron pair to abstract a proton from b carbon of the alkyl halide. The pair of electrons in the C @ H bond becomes the p component of the double bond as the C Br bond breaks. The electrons in the C @ Br bond become an unshared electron pair of bromide ion.
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Unformatted text preview: 5.38 The problem states that the reaction is f rst order in (CH 3 ) 3 CCl ( tert-butyl chloride) and f rst order in NaSCH 2 CH 3 (sodium ethanethiolate). It therefore exhibits the kinetic behavior (overall second order) of a reaction that proceeds by the E2 mechanism. The base that abstracts the proton from car-bon is the anion CH 3 CH 2 S 2 . H C H 1 H CH 3 CH 2 S CH 3 CH 2 S C(CH 3 ) 2 2 Cl Cl H 2 C 1 2 C H CH 3 CH 3 H Br CH 2 (CH 3 CH 2 ) 2 C H 2 N 1 1 2 H H 2 N 2 (CH 3 CH 2 ) 2 C CH 2 Br CH 3 CH 3 CH 2 (CH 3 ) 3 C C(CH 3 ) 3 C(CH 3 ) 3 Cl NaOCH 3 CH 3 OH 4-tert-Butyl-1-methylcyclohexene (95%) 4-tert-Butyl-(methylene)cyclohexane (5%) 1 O CH 3 O CH 3 OCH 2 CH 3 OCH 2 CH 3 O CH 3 O CH 3 O CH 3 O OCH 3 KOH heat O Br O O O O O Br Br KOC(CH 3 ) 3 DMSO (84%) STRUCTURE AND PREPARATION OF ALKENES: ELIMINATION REACTIONS 113...
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This note was uploaded on 09/20/2011 for the course CHM 2210 taught by Professor Reynolds during the Fall '01 term at University of Florida.

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