Final Questions Before the Test!

[ForUs_J&S]

Advertisement - Members don't see this ad

Hi everyone,

I'm taking the exam in a few hours and I am doing a light review to memorize formulas and such. Can you help me answer the following questions? I seem to get conflicting explanations from my resources.

1. When you draw a cyclohexane chair structure and you have a bromine and a methyl group, which one goes equatorial?

2. Does H2SO4 deprotonate fully (both hydrogens deprotonate entirely) or is only the first hydrogen deprotonated fully and the second just slightly deprotonated?

 

[Hushman]

For question one I suggest looking at a table of A values, whichever has the highest A value prefers to go equatorial. So you don't have to go digging, bromines A value is 0.38 and methyls A value is 1.7, therefore methyl will prefer to go equatorial. Remember, the halogens are electronegative and hold onto their electrons tightly and are usually smaller than other groups. I suggest looking over a table of A values to see what the general trends and the tricks are (For example -O-Methyl is actually smaller and will go axial compared to -methyl).

For question two you are correct, the first hydrogen is a strong acid and will deprotonate fully, while HSO4- is a weak acid and you will need to know the ka and the pH to determine how much will be deprotonated.

 

[DAT Destroyer]

Hi everyone,

I'm taking the exam in a few hour and just doing a light review to memorize formulas and such. Can you help me answer the following questions? I seem to get conflicting explanations from my resources

1. When you draw a cyclohexane chair structure and you have a bromine and a methyl group, which one goes equatorial?

2. Does H2SO4 deprotonate fully (both hydrogens deprotonate entirely) or is only the first hydrogen deprotonated fully and the second just slightly deprotonated?

1. Methyl
2. BOTH deprotonate fully

Good luck on your DAT!

Dr. Romano

 

[rak173]

1. Methyl
2. BOTH deprotonate fully

Good luck on your DAT!

Dr. Romano

Doesn't the 2nd H in H2SO4 dissociate partially since HSO4- is a weak base?

 

[DAT Destroyer]

Doesn't the 2nd H in H2SO4 dissociate partially since HSO4- is a weak base?

The second step is quite good, and for your purposes, BOTH essentially come off. For the DAT exam.....If given 0.1 M H2SO4,,,,,,take the - log of 0.2M ......since there are 2 H's. In analytical work, we might take into account the second step as you suggest.....but nevertheless,,,,the answers would be very close.

Dr. Romano

 

[ForUs_J&S]

Thank you everyone for the responses. Both of these weren't tested