6.1.5 - Isomerism

Question 1

Why does trans-1,2-dibromoethane have a higher melting point than cis-1,2-dibromoethane?

Answer 1

More points of contact between trans isomers so intermolecular bonds are stronger.

Question 2

How do you assign E and Z isomers?

Answer 2

Choose atoms or molecules with greatest mass on either side of double bond.
If they are on the same side it’s a Z isomer and if they’re om opposite sides it’s an E isomer.

Question 3

What are structural isomers?

Answer 3

Molecules with the same molecular structure but different structural formula.

Question 4

What are sterioisomers?

Answer 4

Same molecular and structural formula but they still have a different arrangement.
E and z isomers

Question 5

Why can cis/ trans isomerism occur in alkenes but not alkanes?

Answer 5

the c=c double bond leads to restricted rotation so groups cannot move around.
In alkanes, carbon and hydrogen atoms can move freely.