Problem Set 2: Hydrocarbons and Functional groups ANSWER KEY
Chemistry 260
Organic Chemistry
1.
Which of the following statements about ethane is true?
(1)
(2)
(3)
(4)
(5)
the hybridization about carbon is sp²
combustion of ethane is endothermic
ethane is a polar molecule
ethane is insoluble in water
ethane is a liquid at STP
The answer is 4.
2.
The general formula for an alkane is:
(1) CnH2n+4
(2) CnH2n+2
(3) CnH2n
(4) CnH2n-2
(5) CnH2n-4
The answer is 2.
3.
Name the following compound by the IUPAC system: C(CH2CH2CH3)4.
(1) tetrapropylmethane
(3) 1,1-dipropylheptane
(2) 4,4-dipropylheptane
The answer is 2.
The structure of C(CH2CH2CH3)4 is:
CH2CH2CH3
CH3CH2CH2 C CH2CH2CH3
1 2 3
4
CH2CH2CH3
5 6 7
The IUPAC name: 4,4-dipropylheptane
4.
Which of the following is not 3,3-diethylpentane?
(1) C(CH2CH3)4
(2)
(3)
CH2CH3
CH3CH2CCH2CH3
CH2CH3
(4) CH3CH2C(CH2CH3)2CH2CH3
(5) none of these
The answer is 5.
1
C 2H 5
H 5C 2
H 5C 2
C
C 2H 5
All of the structures in choices (1)-(4) represent 3,3-diethylpentane:
CH2CH3
1 2 3 4 5
CH3CH2CCH2CH3
CH2CH3
5.
Give the structural formula of:
(a) 2,2,3,3-tetramethylpentane
(b) 2,3-dimethylbutane
(c) 3,4-dimethyl-4-ethylheptane
CH3 CH3
(a)
CH3C
CCH2CH3
CH3 CH3
CH3
(b)
CH3CHCHCH3
CH3
(c)
CH3
CH3
CH3CH2CH
CCH2CH2CH3
CH2CH3
6.
Give the IUPAC name of:
(a) (CH3)2CHCH2CH2CH3
(b) (C2H5)2C(CH3)CH2CH3
(c)
CH3CH2CHCH2CHCH2CH3
CH3
CH2CH2CH3
(a) 2-methylpentane
(b) 3-ethyl-3-methylpentane
CH3
1
2
3
4
2
3
4
5
CH3CH2CHCH2CHCH2CH3
CH3
CH2CH2CH3
6
5
CH2CH3
5
(c) 5-ethyl-3-methyloctane
1
CH3
3 4
CH3CH2CCH2CH3
CH3CHCH2CH2CH3
1
2
7
8
2
(numbering from other end gives 4-ethyl-6-methyloctane. Numbers of alkyl
substituents are higher ⇒ not the best answer.)
7.
Which of the following formulae represents the primary alcohol?
(1) RCH2OH
(2) RCOOH
(3) R2CHOH
(4) RCO2R
(5) R3COH
The answer is 1.
(1)
(2)
(3)
(4)
(5)
8.
primary alcohol
carboxylic acid
secondary alcohol
ester
tertiary alcohol
How many constitutional isomers are there with the formula C4H10O?
The answer is 7:
CH3CH2CH2CH2OH
CH3
CH3CH2CHCH3
H3C C OH
OH
CH3OCH2CH2CH3
CH3
CH3CHCH2OH
CH3CH2OCH2CH3
9.
CH3CHOCH3
CH3
CH3
Name the following compounds:
(a)
CH3CHCH2CH2OH
Cl
3-chloro-1-butanol
(d)
Cl CH2CH2CH2CH CH2
5-chloro-1-pentene
(b)
CH3CH2CH(OH)CH3
2-butanol
(e)
OH
CH3
C
CH3
C 2H 5
2-methyl-2-butanol
3
(c)
(f)
CH3
H3C CH
C C CH2
H
CH2 Br
CH3CHCH2CH2CH2Cl
CH3
CH3
3-bromo-3,4-dimethyl-1-hexene
1-chloro-4-methylpentane
10.
Draw the structures of all possible constitutional isomers of:
(a) C4H9Cl
(a)
(b) C3H6Cl2
(c) C3H8O
First, go through all the possible functional groups and determine which
ones have molecules of formula C4H9Cl.
Chloroalkane?
An alkane has general formula CnH2n+2. Replace one H with Cl, get CnH2n+1Cl.
For C4, formula is C4H9Cl. Matches formula given in question ⇒ chloroalkane
is a possible structure. ü
Chloroalkene?
An alkene has general formula CnH2n. Replace one H with Cl, get CnH2n-1Cl.
For C4, formula is C4H7Cl. Does not match formula given in question ⇒
chloroalkene is not a possible structure. X
Chloroalkyne?
An alkyne has general formula CnH2n-2. Replace one H with Cl, get CnH2n-3Cl.
For C4, formula is C4H5Cl. Does not match formula given in question ⇒
chloroalkyne is not a possible structure. X
Chlorocycloalkane?
A cycloalkane has general formula CnH2n. Replace one H with Cl, get CnH2n1Cl. For C4, formula is C4H7Cl. Does not match formula given in question ⇒
chlorocycloalkane is not a possible structure. X
Chlorocycloalkene? X
Chlorocycloalkyne? X
The structures are then all the possible chloroalkanes we can draw of
formula C4H9Cl:
4
Cl
CH3CH2CH2CH2Cl
CH3CH2CHCH3
1-chlorobutane
2-chlorobutane
CH3
CH3
(b)
CH3CHCH2Cl
H3C C CH3
1-chloro-2-methylpropane
Cl
2-chloro-2-methylpropane
First, go through all the possible functional groups and determine which
ones have molecules of formula C3H6Cl2.
Dichloroalkane?
An alkane has general formula CnH2n+2. Replace two H with Cl, get CnH2nCl2.
For C3, formula is C3H6Cl2. Matches formula given in question ⇒
dichloroalkane is a possible structure. ü
Dichloroalkene?
An alkene has general formula CnH2n. Replace two H with Cl, get CnH2n-2Cl2.
For C3, formula
is C3H4Cl2. Does not match formula given in question ⇒ dichloroalkene is
not a possible structure. X
Dichloroalkyne?
An alkyne has general formula CnH2n-2. Replace two H with Cl, get CnH2n-4Cl.
For C3, formula
is C3H2Cl2. Does not match formula given in question ⇒ dichloroalkyne is
not a possible structure. X
Dichlorocycloalkane?
A cycloalkane has general formula CnH2n. Replace two H with Cl, get CnH2n2Cl2. For C3, formula is C3H4Cl2. Does not match formula given in question ⇒
dichlorocycloalkane is not a possible structure. X
Dichlorocycloalkene? X
Dichlorocycloalkyne? X
The structures are then all the possible dichloroalkanes we can draw of
formula C3H6Cl2:
5
Cl
ClCH2CH2CH2Cl
CH3CH2CHCl
1,3-dichloropropane
1,1-dichloropropane
Cl
Cl
(c)
CH3CHCH2Cl
H3C C CH3
1,2-dichloropropane
Cl
2,2-dichloropropane
First, go through all the possible functional groups and determine which
ones have molecules of formula C3H8O.
Alcohol?
An alcohol with an alkane backbone has general formula CnH2n+2O. For C3,
formula is C3H8O. Matches formula given in question ⇒ alcohol with alkane
backbone is a possible structure. ü
Alcohol with an alkene backbone has general formula CnH2nO. X
Alcohol with an alkyne backbone has general formula CnH2n-2O. X
Alcohol with a cycloalkane backbone has general formula CnH2nO. X
Ether?
An ether with an alkane backbone has general formula CnH2n+2O. For C3,
formula is C3H8O. Matches formula given in question ⇒ ether with alkane
backbone is a possible structure. ü
Ether with an alkene backbone has general formula CnH2nO. X
Ether with an alkyne backbone has general formula CnH2n-2O. X
Ether with a cycloalkane backbone has general formula CnH2nO. X
Aldehyde?
An aldehyde with an alkane backbone has general formula CnH2nO. For C3,
formula is C3H6O. Does not match formula given in question ⇒ aldehyde
with alkane backbone is not a possible structure. X
Aldehyde with alkene backbone has general formula CnH2n-2O. X
Aldehyde with alkyne backbone has general formula CnH2n-4O. X
Adehyde with cycloalkane backbone has general formula CnH2n-2O. X
Carboxylic acid?
No, because two O atoms in carboxylic acid. X
Ester?
No, because two O atoms in ester. X
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The structures are then all the possible alcohols and ethers with alkane
backbones (i.e. all saturated C-C bonds) of formula C3H8O:
OH
CH3CH2CH2OH
CH3CHCH3
propanol
2-propanol
CH3CH2OCH3
ethyl methyl ether
11.
Elemental combustion analysis of an alcohol gave the following results:
Carbon 68.13%, Hydrogen 13.72%. Possible structures for this alcohol are
(1)
(2)
(3)
(4)
(5)
3-methyl-2-butanol
2-methyl-3-pentanol
2-pentanol
2-methylcyclohexanol
none of the above
The answers are 1 and 3.
Assume we have
C
68.13%
H
13.72%
O
18.15%
100 g of the compound:
68.13 g / 12.01 g mol-1 = 5.67 mol
13.72 g / 1.008 g mol-1 = 13.6 mol
18.15 g / 16.00 g mol-1 = 1.13 mol
Note: the amount of O is found by difference. An alcohol has the general
formula ROH where R = alkyl. Dividing by 1.13 mol and rounding to the
nearest whole number gives: C: 5; H: 12;
O: 1
Therefore, C5H12O is the simplest formula. The possible structures are:
(1) 3-methyl-2-butanol
(3) 2-pentanol
OH
OH
CH3CHCHCH3
CH3CHCH2CH2CH3
CH3
Both fit the simplest formula.
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12.
Josamycin is a macrolide antibiotic produced by the bacteria, Streptomyces
narbonensis. This compound has antimicrobial activity against a wide
spectrum of pathogens. Write the name of each of the circled functional
groups on the lines provided below.
Answers: 1 ester or carboxylic ester, 2 amine, 3 aldehyde, 4 ether, 5 alcohol
13.
Write the name of each indicated functional group in the space provided.
Answers: (1) ester, (2) carboxylic acid, (3) amine, (4) amide.
14.
Draw all constitutional isomers with the molecular formula C5H11Cl. Draw
each structure only once.
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