Question

1. Would the ratio of isomeric heptenes change if potassium tert-butoxide were used in place of DBU? Explain your reasoning.

2. cis-1-Bromo-4-methylcyclohexane undergoes E2 elimination faster than trans-1-bromo-4-methylcyclohexane. Explain your reasoning in terms of mechanism.

3. The lab ran out of xylene. You have your choice of methanol and tert-butanol. Which would you choose and why.

4. When treated with DBU, (1-chloropropyl)benzene and (2-chloropropyl)benzene give the same product but (2-chloropropyl)benzene reacts faster. Explain the results in terms of mechanism.

Answer 1

Answer for question number 1)

No, Because both are strong bases with large steric requirements and are frequently reagents of choice for less substituted product of alkene. The difference between   and DBU (1,8-Diazabicyclo[5.4.0]undec-7-ene) are only tert-butoxide are nucleophilic base and DBU is non nucleophilic base. Therefore there is no change of ratio of isomeric heptenes if potassium tert-butoxide were used in place of DBU.

Answer for question nunber 2)

In case of cis-1-Bromo-4-methylcyclohexane bromine group is on axial position of cyclohexane ring and therefore anti proton is available for axial bromine and antiperiplanar transition state is easily obtain, so elimination occures easily . But in case of trans-1-bromo-4-methylcyclohexane , there is no anti proton present in stable structure but after fliping of ring ellimination occures and conversion from low energy conforrmation to high energy conformation therefore reaction rate is decreases in case of trans isomer . for more understanding refer mechanism; dAnswer for question 3)

My choice is tert-butanol because polarity difference is less between xylene and tert-butanol as compared to xylene and methanol and methanol is dangerous. so i will prefer tert-butanol.

Answer for question 4)

In case of (1-chloropropyl)benzene , chlorine group adjacent to benzene ring and in this reaction base used are very strong (DBU) and its SN2 reaction so hydogen require is acidic hydrogen and adjacent hydrogen to chlorine are beta hydrogen are more acidic in case of (2-chloropropyl)benzene therefore rate of reaction is greater in case of (2-chloropropyl)benzene than (1-chloropropyl)benzene. see mechanism for more understanding: