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Chapter 14 Solutions

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    1112
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    In-chapter exercises

    E14.1:

    image742.png

    E14.2:

    a)

    image744.png

    b) The second nitro group further stabilizes the negatively-charged intermediate (the negative charged can be delocalized to either one of the nitro groups).

    image746.png

    c) The step in which the halogen leaves (the second step) is NOT the rate-determining step in this reaction – the rds is the initial attack by the nucleophile (which temporarily disrupts the aromaticity of the ring). Thus the fact that fluorine is a relatively poor leaving group is inconsequential. A fluorine substituent actually works better than other halogens because it is more electronegative, making the attached carbon more electron-poor and thus a better nucleophile, increasing the rate of the rds.

    E14.3:

    image748.png

    E14.4:

    image750.png

    The cyclohexyl phosphate could form if the phosphate attacked the carbocation intermediate as a nucleophile rather than as a base:

    image752.png

    E14.5:

    image754.png

    image756.png

    image758.png

    E14.6:

    The elimination phase of the gamma-substitution is:

    image760.png

    The addition phase completes the substitution:

    image762.png

    image764.png

    E14.7:

    image766.png

    E14.8:

    The mechanism for the hydrolysis reaction can be depicted:

    image768.png

    The methyl iodide helps to prevent the reverse reaction (thioacetal formation) by serving as an electrophilic 'trap' for the thiol groups:

    image770.png

    End-of-chapter problems

    P14.1: (See Biochemistry 1997, 36, 12526)

    image772.png

    image774.png

    P14.2: This reaction is an elimination followed by enamine to imine tautomerization followed by hydrolysis of the imine.

    image776.png

    P14.3:

    image778.png

    fig 5

    P14.4: A likely mechanism for cysteine 'tagging' is by a Michael addition.Michael addition)

    image780.png

    P14.5:

    a) This is a dehydration followed by tautomerization.

    image782.png

    b) This reaction requires thiamine diphosphate.

    image782a.png

    P14.6:

    image784.png

    P14.7:

    image786.png

    P14.8: Notice that in both reactions the more common E1cb mechanism is not possible, as there is no way to stabilize a carbanion intermediate. However, carbocation intermediates can be stabilized by resonance in both a) and b).

    a) Here, the intermediate carbocation is conjugated (allylic) to the two double bonds in the ring.

    image788.png

    b) Here, the intermediate carbocation is stabilized by electron donation from the adjacent nitrogen.

    image788b.png

    P14.9: This is an E1cb elimination - AMP is the leaving group.

    image790.png

    P14.10:

    a) This is a retro-aldol reaction.

    image792.png

    b) This is something we haven't seen before - a PLP-dependent retro-Claisen. Notice that a carbon-carbon bond is broken.

    image794.png

    image796.png

    image798.png

    c)

    image800.png

    image802.png

    image804.png

    P14.11:

    image806.png

    P14.12:

    image808.png

    P14.13:

    image810.png

    P14.14: Notice that in order for the (E)-alkene to form, the C-H and C-Br bonds must be anti and co-planar.

    image812.png

    P14.15: Recall that for an E2 reaction to occur on a cyclohexane ring, the leaving group and the abstracted hydrogen must both be in axial positions.

    image814.png

    P14.16:

    image816.png

    image818.png

    image820.png

    image822.png

    image824.png

    P14.17:

    image826.png

    image828.png

    P14.18:

    image830.png

    P14.19:

    a)

    image832.png

    b)

    image834.png

    P14.20:

    image836.png

    Challenge problems

    C14.1:

    a) It is a decarboxylation reaction, but there is no obvious way for the electron pair to be stabilized.

    image838.png

    b) A carbene intermediate would imply a very hydrophobic active site pocket – see Chemical and Engineering News, May 12, 1997, p. 12; Science 1997, 276, 942.

    c) See Chemical and Engineering News, March 13, 2000, p. 42.

    C14.2: See Biochemistry 2003, 42, 248 (scheme 1)

    C14.3: The first part is cyclic imine formation, then we see an E1cb dehydration adjacent to the imine.

    image840.png

    C14.4:

    a) Lacking any other information, it is reasonable to expect a mechanism that parallels that of asparagine synthetase (section12.2B): conversion to an acyl phosphate, then acyl transfer with ammonia nucleophile.

    b) The nitrogen comes from the amino group on aspartate, and is freed by the final elimination step.

    image842.png

    C14.5: See European J. Biochem. 2002, 269, 1790, fig 7.

    Organic Chemistry With a Biological Emphasis by Tim Soderberg (University of Minnesota, Morris)


    This page titled Chapter 14 Solutions is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.


    This page titled Chapter 14 Solutions is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Tim Soderberg via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.