Question

please help with 16-18 thank you!

NBS Ahv/ROOR ? 16. How many constitutional isomer allylic bromides does the following reaction give? a. 3 b. 4 c. 5 d. 6 e, not a.-d. 17. Ignoring stereochemistry, what is the overall enthalpy difference of the reaction of 3-ethylpentane, fluorine, and light going to the major mono-fluorinated product? Bond Disassociation Energies kcal/mole C-H C-F C-CIC -Br C- I X -X 1° 98 107 81 68 53 F 38 2° 95 106 80 68 53 ci 58 30 | 91 106 79 65 50 Br 46 36 H-X 136 103 88 71 Selectivity Ratios 1° 2° 3° F 1 1.2 1.4 c 1 4 5 Br 1 80 1700 | a. -107 b.-109 C. -111 d. -113 e, not a.-d. 18. Which step in the previous reaction is least exothermic but not endothermic!? a. initiation b. first propagation c. second propagation d. termination giving the same major producte. not a.-d. o

Answer 1

16) Answer is a). Since three allylic positions are present in molecule hence it give three constitutional isomers but also have configurational isomers.

17) Answer is d).

Reaction involve cleavage of 3° C-H bond and F-F bond and involve formation of C-F bond and H-F bond.

Thus, ∆H = ∆H(bond cleaved) - ∆H (bond formed)

= ∆H {3°(C-H)} + ∆H(F-F) - ∆H(C-F) - ∆H (H-F)

= 91 + 38 - 106 - 136

= -113

18) Answer is b)..