Kaplan Ochem Mistake?

[jenk329]

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For all those who have done Kaplan's "before the test" last practice exam, #80 on the ochem section goes a little something like this..
"Which of the following is true regarding the relative melting point and boiling points of the cis and trans 1,2-dichloroethane?"
a. the melting and boiling points of the cis isomer are higher
b. the mp of the cis isomer is higher and the bp of the trans isomer is higher.
c. the mp of the cis isomer is lower and the bp of the trans isomer is lower.
d. the mp and bp of the cis isomer are higher

Kaplan says its choice D, but then seems to contradict itself in the answer-explanation box by saying C is correct, which I chose...
Has anyone else come across this contradiction....just to be sure C is correct right? Thanks!

 

[dentwannabe]

For all those who have done Kaplan's "before the test" last practice exam, #80 on the ochem section goes a little something like this..
"Which of the following is true regarding the relative melting point and boiling points of the cis and trans 1,2-dichloroethane?"
a. the melting and boiling points of the cis isomer are higher
b. the mp of the cis isomer is higher and the bp of the trans isomer is higher.
c. the mp of the cis isomer is lower and the bp of the trans isomer is lower.
d. the mp and bp of the cis isomer are higher

Kaplan says its choice D, but then seems to contradict itself in the answer-explanation box by saying C is correct, which I chose...
Has anyone else come across this contradiction....just to be sure C is correct right? Thanks!

I just did this yesterday. Kaplan doesn't contradict itself.
from what I read, Kaplan says, the cis will have higher boiling point since it has dipole moment.
And Kaplan says since melting point depends on structural stability, since trans is packed more tightly, it will have a higher melting point.

So choice C is CORRECT, since it says mp of cis will be lower than mp of trans AND bp of trans will be lower than bp of cis.

i think i had the same problem as u... jus gotta read this bitchy questions carefully.

OH YEA, im taking mines tommorrow.. im gonna take my last topscore one today.. then 12:30 tommorrow is JUDGEMENT DAY!! 😱

 

[mochafreak]

I'm pretty sure C is correct. The cis is polar so it has a higher bp, and the trans is more symmetrical which allows for better packing and increases the melting point.

 

[LMav]

For all those who have done Kaplan's "before the test" last practice exam, #80 on the ochem section goes a little something like this..
"Which of the following is true regarding the relative melting point and boiling points of the cis and trans 1,2-dichloroethane?"
a. the melting and boiling points of the cis isomer are higher
b. the mp of the cis isomer is higher and the bp of the trans isomer is higher.
c. the mp of the cis isomer is lower and the bp of the trans isomer is lower.
d. the mp and bp of the cis isomer are higher

Kaplan says its choice D, but then seems to contradict itself in the answer-explanation box by saying C is correct, which I chose...
Has anyone else come across this contradiction....just to be sure C is correct right? Thanks!

Yes, C is the right choice.

 

[dat_student]

For all those who have done Kaplan's "before the test" last practice exam, #80 on the ochem section goes a little something like this..
"Which of the following is true regarding the relative melting point and boiling points of the cis and trans 1,2-dichloroethane?"
a. the melting and boiling points of the cis isomer are higher
b. the mp of the cis isomer is higher and the bp of the trans isomer is higher.
c. the mp of the cis isomer is lower and the bp of the trans isomer is lower.
d. the mp and bp of the cis isomer are higher

Kaplan says its choice D, but then seems to contradict itself in the answer-explanation box by saying C is correct, which I chose...
Has anyone else come across this contradiction....just to be sure C is correct right? Thanks!

Depends on the structure and lots of other factors. In this case, the cis form has a higher boiling point and the trans has a higher melting point. C is the right answer.