| Qu 1: |
Using the following average bond energies, estimate
the strength of the π bonds in an alkyne and
an alkene |
|
C≡C = 820 kJ/mol (196 kcal/mol), C=C = 611 kJ/mol (146 kcal/mol), C-C = 368 kJ/mol (88 kcal/mol) |
| |
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| Qu 2: |
Consider the following points about the reaction of
2-butyne with HBr |
|
(i) reaction with 1 equivalent gives 2-bromo-2-butene
(ii) reaction with excess gives 2,2-dibromobutane |
|
(a) What conclusions can you reach about the reactivity
of 2-bromo-2-butene compared to 2-butyne ? |
|
(b) Consider the two possible carbocations that could
be formed in the conversion of 2-bromo-2-butene to 2,2-dibromobutane. Suggest
a reason for the observed regioselectivity. |
|
|
| Qu 3: |
What would be the product from the reaction of propene
with following reagent sequence: |
|
(i) Br2 (ii) excess NaNH2 , heat followed by H2O (iii)
NaNH2 then MeI |
|
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| Qu 4: |
Show the major products, with stereochemistry where
applicable, for the reactions of : |
|
(a) 1-pentyne and (b) 2-pentyne with each of the following
: |
|
| (i) H2 / Lindlar Pd |
(v) excess HCl |
| (ii) excess H2 / Pd |
(vi) aq. H2SO4, HgSO4 |
| (iii) Na / NH3 |
(vii) Br2 |
| (iv) 1 equiv. HCl |
(viii) O3 then H2O |
|
