241 CHEM Synthesis & Reactivity I Exam #1 - February 13, 2006
Name:_____KEY____________ Lab Section: M T F
This exam ends at 9:25 am as indicated by the clock in Althouse 108. In the space provided, give the best answer (3 points each) __A__
a) HC C
1. Which of the following is not an isomer of C6H10?
CH3 c)
b)
d)
__B__
2. What is the correct IUPAC name for the following compound?
Cl a) 3-chloro-4-ethyl-2-isopropylhexane b) 4-chloro-5-ethyl-2,3-dimethylheptane c) 3-chloro-4-ethyl-1,1,2-trimethylhexane d) 4-chloro-3-ethyl-2-isopropylhexane
__B__
3. pKa values of a series of compounds are listed below. Which would be deprotonated by NaOH? A B C D (CH3)3COH NH3 HC CH CH3CO2H
pKa 25 4.7 18 33
__C__
4. Which of the following is not a resonance structure of the cation at left?
a) OCH3 b)
__D__
OCH3 OCH3
c)
OCH3 OCH3
d)
5. Which of the structures below contains an oxygen with a formal charge of +1?
:
:O : a) CH3 OH CH3 d) CH3 O : CH3
b) CH3 O :
c)
O:
:
:
__D__
6. The three staggered conformations of 2-methylbutane are shown below:
H H CH3 CH3 H CH3 I H CH3 H CH3 H H H CH3
H CH3 II
CH3 CH3 III
Which structure represents the most populated conformation? a) I c) III b) II d) Both I and II __B__ 7. Which molecule below is not 1-chloro-3-methylbutane? H C CH CH2CH2Cl a) 3 c) CH3 Cl
b) H H Cl H d) ClCH2CH2CH(CH 3)2
H CH2CH3
__A__
8. The 3 molecules below are all 1,2-dibromocyclohexane. Which accurately represents cis1,2-dibromocyclohexane?
H Br A
__C__
H H Br Br B H Br Br H C
H Br D both B and C
9. Which form of carbon below could be a Lewis acid? a) CH4 b) CHCl3 c) CH3+ d) CH3-
__B__
10. The most stable conformation of cis-1-tert-butyl-2-methylcyclohexane is the one in which: a) the tert-butyl group is axial and the methyl group is equatorial b) the methyl group is axial and the tert-butyl group is equatorial c) both groups are axial d) both groups are equatorial
Short Answer: (points as indicated) 11. Name the following compounds according to IUPAC rules. (3 points each)
5-ethyl-2,4-dimethyloctane
Cl 2-bromo-3-chloro-3-methylpentane Br
NH2 3,4-dimethylcyclodecylamine OR 1-amino-3,4-dimethylcyclodecane
12.
Neatly draw a skeletal structure that accurately depicts each of the following molecules. (3 pts each) a) 4-isopropylheptane
b) butylcycloheptane
c) cis-3-ethylcyclohexanol
OH or OH
13.
a) On the flat ring cyclohexane below, attach methyl groups to clearly show the 3-dimensional structure of cis-1,4-dimethylcyclohexane. (4 points)
CH3
CH3
b) Now, draw the two chair conformations of cis-1,4-dimethylcyclohexane and label them I and II. Be sure that your drawings clearly show axial and equatorial groups. (6 points)
CH3 H H I CH3 CH3 H II
CH3 H
c) How many gauche interactions are present in each conformation? (4 points) I: ____2_____ gauche interactions II: ___2______ gauche interactions
Recalling that each gauche interaction "costs" 3.8 kJ/mol (or 0.90 kcal/mol), determine G for the conversion of I to II. (4 points)
G = 0 kJ/mol
(no difference in stability)
14.
Benzoic acid is depicted below.
O OH pKa = 4.5
a) Give 2 reasons why the most easily removed H is on the oxygen and not on one of the carbon atoms. (4 points) hydrogen is more acidic when attached to an electronegative atom resonance stabilization of oxygen anion by moving charge to other oxygen
b) Which compound below would produce a conjugate base that is suitably strong enough to remove the acidic H on benzoic acid? Explain. (4 points)
HCl -7 NaHSO4 2.0 HCN 9.2 HF 3.2
CN- is the only conjugate base strong enough to deprotonate benzoic acid because it's the only one that will result in a weaker acid-base pair.
O OH + CNO O+ HCN
weaker acid and base
c) In lab, benzoic acid was dissolved in CH2Cl2. When this solution was mixed with water, most of the benzoic acid remained in the CH2Cl2 layer. But when mixed with NaHCO3, little of the benzoic acid was found in the CH2Cl2. Explain these results. (4 points) Benzoic acid is soluble in CH2Cl2 but not in water. When benzoic acid mixes with NaHCO3, an acid base reaction occurs, producing sodium benzoate, a salt. The salt is soluble in water, explaining why no benzoic acid remains in the CH2Cl2.
15.
Tamiflu is an antiviral drug that is believed to be the only effective treatment for the avian flu that has shown signs of emerging in Asia.
O O O N H OC2H5 NH2 Tamilflu
a) Label the circled functional groups. (8 points)
ether O amide O O N H OC2H5 NH2 ester
amine
b) Several atoms are labeled with stars (*). Indicate the hybridization these atoms. (4 points)
sp3
* O O * N H sp3 NH2 *
* O OC2H5 sp2
sp2
c) For the carbon atoms that are boxed, label each as 1, 2, 3 or 4. (4 points)
2 O O 1 2 O N H OC2H5 NH2 2