5 Steps to a 5 AP Chemistry 2019

Organic Chemistry ❮ 281

HC

H

H

C

H

H

C

H

C

C

H

H

C

H

H

H

HH H

HC

H

H

CC

H

H

C

H

H

H

HC

H

H

C

H

C

C

H

H

C

H

H

C

H

H

H

HH H

C

HH H

C

HHH

HC

H

H

CC

H

C

H

H

H

C H

HH H

C

HHH

These compounds are 2-methylpentane; 3-methylpentane; 2,2-dimethylbutane;

and 2,3-dimethylbutane, respectively. These four, along with the original n-hexane, are

the only isomers. If you think you have another isomer, you have simply redrawn one

of these. Try naming your answer and see if it matches one of these names.

Total your points. There are 10 points possible. Subtract 1 point if your answers

do not have the correct number of significant figures.

Question 2
Note that, while organic chemistry is not an AP topic, all the materials in these questions
depend on basic AP chemistry knowledge, which is why this chapter can be valuable.

(a) As shown below, there are two different resonance forms. You only need to draw one
of these.

H N

H

H

H

Ca Cb Ob−

H Oa Oa−

H N

H

H

H

Ca Cb Ob

H

or

You get 1 point for a correct Lewis structure around the nitrogen and carbon

atoms. You get 1 point for a correct Lewis structure around both oxygen atoms.

(b) There are two acceptable resonance forms, differing only in the bonding to the oxygen
atoms (and hence their formal charges). For an atom, the formal charge = valence
electrons – nonbonding electrons – ½ (bonding electrons).
The formal charges for the left structure are in the following table. For the other
structure, simply reverse the lines for Oa and Ob.

N 5 – 0 – ½ (8) = +1

Ca 4 – 0 – ½ (8) = 0

Cb 4 – 0 – ½ (8) = 0

Oa 6 – 4 – ½ (4) = 0

Ob 6 – 6 – ½ (2) = –1

You get 1 point for a correct set of formal charges and 1 point if the total of all the

formal charges is 0.

Total your points. There are 4 points possible.