I have some questions for those of you that have done AAMC#7 Bio.

#163
A student uses thin layer chromatography on silica plates to monitor the progress of the reaction below. Does the product have a higher or lower Rf than the starting material?

.........NaBH4
Ph=O --------> Ph-OH

a)higher because the product is more polar than the starting material
b)higher because the product is less polar than the starting material
c)lower because the product is less polar than the starting material
d)lower because the product is more polar than the starting materal

I put (A), but the answer key says (D). I thought polar molecules travel faster than non(less)polar molecules, thus have higher Rf?
__________________________________________________ _______________
#166
Embryonic mouse cells divide every 10 hours at 37 degrees C. How many cells would be produced from an egg after three days?

a)fewer than 50
b)between 50 and 500
c)between 500 and 5000
d) more than 5000

I put (B), but the answer key says (D).
__________________________________________________ ______________
#171
The IR spectrum of Compound 8 (some molecule in passage) shows hydroxyl and carbonyl absorptions, respectively, at approximately:

a)1700 and 2250
b)1700 and 3400
c)3400 and 2250
d)3400 and 1700

I put (D) but the answer key says (B).


It seems like there are errors in the solution and the explanations doesn't seem to match up with questions. Any thoughts on these question?

If I get these question right, I can get 12 on this section and be a good confidence booster. :)

I think there is an error with 166 and 171 :confused: but for 163 polar substances travel slower on the TLC plate so D is the correct answer. Good luck on it and wish me one as well!

I have some questions for those of you that have done AAMC#7 Bio.

#163
A student uses thin layer chromatography on silica plates to monitor the progress of the reaction below. Does the product have a higher or lower Rf than the starting material?

.........NaBH4
Ph=O --------> Ph-OH

a)higher because the product is more polar than the starting material
b)higher because the product is less polar than the starting material
c)lower because the product is less polar than the starting material
d)lower because the product is more polar than the starting materal

I put (A), but the answer key says (D). I thought polar molecules travel faster than non(less)polar molecules, thus have higher Rf?
__________________________________________________ _______________
#166
Embryonic mouse cells divide every 10 hours at 37 degrees C. How many cells would be produced from an egg after three days?

a)fewer than 50
b)between 50 and 500
c)between 500 and 5000
d) more than 5000

I put (B), but the answer key says (D).
__________________________________________________ ______________
#171
The IR spectrum of Compound 8 (some molecule in passage) shows hydroxyl and carbonyl absorptions, respectively, at approximately:

a)1700 and 2250
b)1700 and 3400
c)3400 and 2250
d)3400 and 1700

I put (D) but the answer key says (B).


It seems like there are errors in the solution and the explanations doesn't seem to match up with questions. Any thoughts on these question?

If I get these question right, I can get 12 on this section and be a good confidence booster. :)

I think there is an error with 166 and 171 :confused: but for 163 polar substances travel slower on the TLC plate so D is the correct answer. Good luck on it and wish me one as well!


When determining polarity here can you look at the respective shifts on C NMR to get an idea?

Thanks,

I think there is an error with 166 and 171 :confused: but for 163 polar substances travel slower on the TLC plate so D is the correct answer. Good luck on it and wish me one as well!
Yeah, I reviewed o-chem again and you are right, polar molecules travel slower on TLC. O-chem is my weakest strength. :scared: I think I need to do slightly more reviews on Friday.

Good luck to you too. :thumbup:

There is definitely an error with the solutions for #166 and #171 (Give yourself +2 points!) if you are using the TPR solutions. Others gave you good explanations for the TLC problem...