Organic Chemistry Test Questions

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  • Topic: Methane, Lewis structure, Ammonia
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1_____2_____3_____4_____5_____6_____7_____8_____9_____TOTAL________ CHEM 237, FALL 2007 HOUR EXAM 1 Name________________________________________________________ TA Name _______________________ __& Section # _________________ Student #______________________________________________________

1. (9 pts) Write a valid Lewis structure for each of the following. Show lone pairs and formal charges where necessary. Draw covalent bonds as lines. (a) bisulfate ion, HSO4-

O HO S O
(b) hydrogen cyanide, HCN

O

H C

N

(c) hydrazoic acid, HN3 (arranged HNNN)

H N

N

N

or

H N

N

N

2. (10 pts) Indicate which of the following pairs do not constitute resonance structures by drawing an “X” in the space provided?

O CH3C-O O

-

O and

-

CH3C O OH

CH3C-OH O CH3CCH3

and

CH3C O OH CH3C CH2

X X X X

and and and

-

CH2CH CH 2 HOCN

+

CH2 CH CH2

HNCO

3. (8 pts) What is the hybridization of the Carbon indicated in bold in the following compounds? H2C=O

sp2

C

sp2

H

C C

Br

sp

CBr4

sp3

4. (10 pts) Malonic acid, HO2CCH2CO2H, is a diprotic acid. The pKa for the loss of the first proton is 2.83; the pKa for the loss of the second proton is 5.69. (a) Explain why malonic acid is a stronger acid than acetic acid (pKa = 4.75). (b) Explain why the anion, -O2CCH2CO2H, is so much less acidic than malonic acid itself. (a) electron withdrawing –CO2H group stabilizes charge of conjugate anion (b) molecules doesn’t want to be dianion

5. (11 pts) Carey. All the parts of this problem refer to the alkane having the carbon skeleton shown.

(a) (2 pts) What is the molecular formula of this alkane? C13H38

(b) (2 pts) What is the IUPAC name? 5-ethyl-2,6-dimethylnonane 1 pt for or 1 pt for 5-ethyl-4,8-dimethylnonane 2,6-dimethyl,5-ethylnonane

(1 pt) How many methyl groups are present in this alkane?____5 (1 pt) How many methylene groups?______5______ (1 pt) How many methine groups?_________3___ (1 pt) How many carbons are primary?______5____ (1 pt) How many are secondary?_____5_______ (1 pt) How many are tertiary?________3___ (1 pt) How many are quaternary?______0______ 6. (8 pts) Carey. Female tiger moths signify their presence to male moths by giving off a sex attractant (pheromone). The sex attractant has been isolated and found to be a 2-methyl-branched alkane having a molecular weight of 254. What is this material?

C18H38

(12 X 18) + 38 = 254

2-methylheptadecane also OK as is CH3(CH2)14CH(CH3)2 7. (6 pts). Write the products of the following reactions indicated by curly arrows.

H H BH2 BH2

H CH3 CH2

8. (14 pts) Carey. Write structural formulas for all the constitutional isomers have the give formulas. (a) C3H4

H 2C

C CH2

HC

C CH3

(b) C3H9N CH3CH2CH2NH2 CH3CH2NHCH3

CH3 H3C N CH3

H3C
C

NH2

H3C

9. (12 pts) Below are 9 structures of compounds with four atoms, one H, one C, one N, and one O. Lone pairs and formal charges have not been added. Circle the pairs that are resonance structures after elaboration of Lewis structures.

+ + + +

+

Resonance pairs are

B,F

D,E

H,I

10. Carey. (8 pts) Rank the following in order of decreasing acidity.

O+ H

N H HO CH3 H

N+ CH3

1 1
most acidic

2 4

3 3

4 2
least acidic

11. (4 pts) Carey. What are the formulas of the following:
O OCCH3 H N O

OCCH3 aspirin C10 H10O4 O O

N H indigo

C16 H10N2 O2

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