names and structures of carbon compounds

sample answers
structural formulae and constitutional isomers (revision of chem 1 if needed)

1. Draw a structural formula (showing all bonds and lone pairs) for the following substances:

C2H5Br N2H4 CCl2O HCOOH

H H xx oo
x x
oo
xo xo xo
H xo N N H
x
o
x
o Clx x HoC o
xoO
H xo C o Br o
x
o C x x
xoxo Cx O
x
xo oo
xo xo xo
H H Cl O
o
o
o
H
H H oo

bromoethane hydrazine phosgene methanoic acid

(rocket fuel) (WW1 poison gas) (formic acid – ants)

2. How many different compounds are represented by the following structural formulae?

H H Cl H Cl H Cl Cl H H H Cl H Cl
H C C Cl H C C H Cl C C H H C C H Cl C C Cl H C C H H C C H
Cl H Cl H H H H H H H H Cl Cl H
two: 1,1-dichloroethane and 1,2-dichloroethane. Notice that cis/trans isomers are not possible around a single bond.

3. Each molecular formula represents the indicated number [n] of constitutional isomers.
Write a full structural formula (showing all bonds and lone pairs) for each isomer:

C6H14 [5] C3H6Cl2 [4] C3H9N [4] C4H10O [7]

hexane 1,1-dichloropropane 1-aminopropane 1-butanol
2-methylpentane 1,2-dichloropropane 2-aminopropane 2-butanol
3-methylpentane 1,3-dichloropropane N-methylethylamine 2-methyl-1-propanol
2,2-dimethylbutane 2,2-dichloropropane trimethylamine 2-methyl-2-propanol
2,3-dimethylbutane 1-methoxypropane
2-methoxypropane
ethoxyethane

abbreviated structural formulae

1. Expand the following abbreviated structural formulae to show all the atoms, bonds and lone pairs.

H H
H H O O H
H H o o C
H H O H H O H o o
H C H H C H
C H
H C C C C H H C C H H C C C C H C H H C C C C C H
C
H C H H H H H C
H H H H H H H
H H H H H

2c-06s tutorial (structures, stereoisomers, intermolecular forces and physical properties) sample answers sample answers to revision tutorial examples, page 1
 2. Structural formulae are commonly abbreviated as follows to enable them to be typed as part of a line
of text (eg in “SI Chemical Data” pages 90-110). Expand the following to full structural formulae, to
show all the atoms, bonds and lone pairs. To what family does each belong?

CH2ClCH2Cl (CH3)3COCH3 CH3COOC2H5 (CH3)3CCOCH3

H H CH3 H H H H CH3 H
oo oo
H C C H H3C C O C H H C C O C C H H3C C C C H
oo oo
o o o o
o Cl
oo
Cl
o o
oo
o CH3 H H ooO oo H H CH3 oo Ooo H
a haloalkane an ether an ester a ketone

What do you think the authors of “SI Chemical Data” mean by this abbreviation (p 90 in 5th ed):
H H
CH2(CH2)4CH2 cyclohexane H C
H
H C C H
H C C H
C H
H
H H

functional groups and families of organic compounds

1. Draw a full structural formula (showing all atoms, bonds and lone pairs)
for at least one example of each of the following.
a) A cycloalkane with four carbons cyclobutane; methylcyclopropane
b) An alkyne with four carbons 1-butyne; 2-butyne
c) An alcohol with three carbons 1-propanol; 2-propanol
d) An amine with two carbons ethylamine C2H5NH2 ; dimethylamine (CH3)2NH
e) An ester with four carbons C2H5COOCH3; CH3COOC2H5; 2 x HCOOC3H7
f) An ether with four carbons methyl propyl, methyl isopropyl, & diethyl ethers
H
H
C HH
g) An aldehyde with four carbons butanal; 2-methylpropanal
O C C C H
h) A ketone with four carbons butanone H O H H
(j)
O H H H
i) A tertiary amine with three carbons trimethylamine O C C C C H
H H H H
j) A carboxylic acid with four carbons butanoic acid; 2-methylpropanoic acid
H H H H H H H H H H H H
H H H
H C C H H C H H H H
CH 3 H C C C H H C C N H
C H C C C O H C N C H
H C C H H C C C C H H C C C C H
C H H O H (d)
H (c)
H H H H H H H H
H H H H H H H H
(a) (b)
H
H H
O H H H C HH
H H H H H
H O H H O C HH H H C C C C HH C C C H
H C O C C C H H
H C O C C C H H C O C C H H C HH (g) H H H O H H
H H H H H H H H
H (f ) H C O C C H
(e)
H H H H H
H O H H H H
O H H H H H H H O H H
H C C O C C H H C H
H C C O C C H H C O C C C H H C C C C H
H H H H H C N C H
H H H H H H (h) H H H (i)
H H
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2. Each of the following substances has more than one functional group. Circle each functional
group present, and label it with with name of the family that the functional group is characteristic
of.
arene ester
CH3
amine H2N COCH2CH3
CH2 CH NH2
O arene amine
benzocaine amphetamine
a local anaesthetic a stimulant

carboxylic acid
amide
COOH
HO NHCOCH3
arene OCOCH3 phenol
ester arene
aspirin paracetamol
an analgesic and antipyretic an analgesic and antipyretic

alkene
alkene
O alkynes
arene aldehyde
amine carboxylic acid
H COOH
OH O HN
cinnamaldehyde O
the flavour of cinnamon
OCH3
phenols
ester O CH3 ethers
CH3 C O CH2 CH2 N+ CH3 OH O OH
CH3 organic arenes
ketone phenol
ammonium ion
acetylcholine dynemicin A
a neurotransmitter an anticancer drug

relating structures and names

1. Draw structural formulae of the following compounds. Identify the functional group(s) present,
and the family or families of carbon compounds to which each compounds belongs.
a) 2-methyl-2-propanol CH3
CH3CCH3 CH3CH2CCH2CH3 CH3CHC CCH2CH2CH3
b) 3-pentanone
OH O CH3 alkyne
c) 2-methyl-3-heptyne a b
alcohol ketone c

d) 3-methylbutanal O O
CH3CHCH2C CH3CHC CH3COCH2CH3
e) 2-aminopropanoic acid CH3 H NH2 OH O
aldehyde ester
d e amine; f
f) methyl ethanoate (methyl acetate) carboxylic acid
g) ethyl methyl ether
CH3OCH2CH3 CH3CH2NCH2CH3
h) diethylamine ether
g H amine
h

2c-06s tutorial (structures, stereoisomers, intermolecular forces and physical properties) sample answers sample answers to revision tutorial examples, page 3
2. Write systematic names (according to the IUPAC rules) for the following compounds.
Identify the functional group(s) present, and their family or families.

CH3 C C CH2
CH3CH2CCH3 CH3CH2CHO
CH3 CH2 CH CH3
O
(a) 5-methyl-2-heptyne (b) butanone (c) propanal
(alkyne) (ketone) (aldehyde)

CH3CH2COCH2CH3 CH2(NH2)CH2COOH CH3CH(OH)CH2COOCH3

O
(d) ethyl propanoate (e) 3-aminopropanoic acid (f) methyl 3-hydroxybutanoate
(ester) (amine; carboxylic acid) (alcohol; ester)

stereoisomerism (E,Z- or cis/trans isomerism in alkenes)

1. Using the isomers of C2H2Cl2 as examples, illustrate the difference between

constitutional isomers and stereoisomers.

constitutional
H Cl H Cl H H
C C C C C C
H Cl Cl H Cl Cl

stereoisomers

2. Why are there stereoisomers for C2H2Cl2 but not for C2H4Cl2? rotation is possible around single
bonds but not double bonds

3. Write the structures of the following alkenes showing the correct >C=C< bond angles.
Draw and name any stereoisomers using both the E,Z and cis and trans conventions.
CH2=CHCH2CH3 CH3CH2CH=CHCH3 1,3-dichloropropene

H C2H5 C2H5 CH3 C2H5 H Cl H H H

C C C C C C C C C C
H H H H H CH3 H CH2Cl Cl CH2Cl
no stereoisomers Z-2-pentene E-2-pentene Z-1,3-dichloropropeneZ-1,3-dichloropropene
E-1,3-dichloropropene E-1,3-dichloropropene

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4. Draw structures for a pair of alkene stereoisomers with following molecular formulae.
Name each substance you have drawn using the E,Z convention.
(a) C3H5Cl (b) C6H12

H CH3 Cl CH3 H CH2CH3 H H

C C C C C C C C
Cl H H H CH3CH2 H H3CH2C CH2CH3
E-1-chloropropene Z-1-chloropropene E-3-hexene Z-3-hexene
(no other pairs possible) (two other pairs possible)

5. Attempt to draw structures of the following alkenes.

CH3
Which of the names below is not valid? Why? CH3 CH2CH3 CH3 CH
CH3
C C C C
(a) E-2,3-dimethyl-2-pentene
CH3 CH3 H CH3
(b) Z-3,4-dimethyl-2-pentene 2,3-dimethyl-2-pentene Z-3,4-dimethyl-2-pentene
(no stereoisomers)

6. Would you expect E- and Z-2-pentene to have identical (a) boiling points; (b) densities?
Neither their bp or densities are the same. They have different molecular shapes, so their
intermolecular forces (hence bp) and ability to pack together (hence densities) will be different.

stereoisomerism involving optical activity (chirality and the R,S- convention)

1. What is optical activity? What kinds of compound are optically active?

Compounds whose molecules are chiral (different from their mirror images) are optically active,
ie cause the plane of plane-polarised light to rotate.

2. Briefly explain the meaning of the following symbols and terms:

(+)- (−)- [α]D chiral dextrorotatory
(+)- rotates polarised light to the right (= dextrorotatory); (-)- rotates polarised light to the left;
[α]D (specific rotation); chiral = not superimposable on its mirror image

3. When is an atom a chirality centre? when bonded to 4 different atoms or groups

Label with an asterisk (*) the stereogenic atoms in the following structures (not all the structures
have a chirality centre). Which of these compounds are optically active?

OH O OH CH3 CH CH2
CH3 C
CH3CH2CHCH3 CH3CHCOOH Cl Cl
H

2c-06s tutorial (structures, stereoisomers, intermolecular forces and physical properties) sample answers sample answers to revision tutorial examples, page 5
4. Draw a structure for an optically-active compound with each of the following molecular
formulae; label the chirality centre in each structure with an asterisk:
CHBrClF C2H4BrCl C5H11Br C7H16

Cl Cl Br CH3
Br C F Br C CH3 CH3 C CH2CH2CH3 CH3CH2 C CH2CH2CH3
H H H H

5. For the following chirality centres, arrange the substituents in priority order (according to the
Cahn-Ingold-Prelog rules), then determine whether the configuration is R or S.

F H CH3 H HO H
C C C
Br CH2CH2CH2CH3 H2N COOH OHC CH2CH3

R- S- S-
Br > F > C4H9 > H NH2 > COOH > CH3 > H OH > CHO > C2H5 > H

6. What are enantiomers? Draw the enanantiomers of the compounds above. Are they R or S?
Enantiomers are molecules which are non-superimposable mirror images of each other. Each
stereogenic atom has the opposite configuration in the enantiomer :

H F H CH3 H OH
C C C
CH3CH2CH2CH2 Br HOOC NH2 CH2CH3 CHO

S- R- R-

7. Using dotted and wedge bonds to show three-dimensional structure,

give structural formulae of the following compounds:

R-2-chloropentane S-3-chloro-3-fluoropropene S-1,2-propanediol

Cl F OH
CH3 C CH2CH2CH3 CH2 CH C Cl HOCH2 C CH3
H H H

8. Which of the following properties of S-lactic acid and R-lactic acid are expected to be identical:
melting point, boiling point, solubility in water, taste, specific rotation ([α]D), magnitude of
specific rotation? Explain briefly. Mp, bp identical because molecules pack in the same way.
Specific rotation equal in magnitude but opposite directions.
Tastes differ since different interaction with proteins (chiral)

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9. Is it possible to predict the direction R-2-bromobutane rotates polarised light?
Not in a simple way. It could be (+)- or (-)-. The label “R” is merely the result of a convention for
labelling the 3-dimensional arrangement of groups around the stereogenic atom.

10. What is a racemic mixture (or racemate)? Why is a racemate difficult to separate?
An equal mixture of a pair of enantiomers. Racemates are usually formed in chemical reactions
in which an atom becomes stereogenic. Enantiomers have identical physical properties, so
cannot be separated on the basis of different solubilities, mp or bp.

11. Is it true that every racemic mixture has the same [α]D? Explain.
Yes, since racemates always have zero rotation .. the individual rotations of the enantiomers
cancel exactly.

12. What is (±)-2-butanol? Could it accurately be described as any of the following:

(c) a mixture containing (+)-2-butanol?

13. Which statement is true of the melting point of racemic 2-aminopropanoic acid (alanine):
(d) it cannot be reliably predicted from the properties of the R- and S- isomers.

14. Molecules of 2-bromo-3-chlorobutane have two chirality centres, each of Br Cl

which can be in the R- or S- configuration. The 2R, 3S- isomer is shown here. H3C C C CH3

(a) How many stereoisomers are there altogether? four H H

(b) List the stereoisomers by name (2R, 3S-, etc); show any mirror-image relationships.
2R,3R 2S,3S
(c) Which of these stereoisomers is likely to be optically active? all four
2R,3S 2S,3R
(d) Is any of the stereoisomers a meso isomer? no

15. Molecules of 2,3-dibromobutane have two chirality centres, each of which Br Br

can be in the R- or S- configuration. The 2R, 3S- isomer is shown here. H3C C C CH3
(a) How many stereoisomers are there altogether? three H H
(b) List the stereoisomers by name (2R, 3S-, etc); show any mirror-image relationships. 2S,3R

(c) Which of these stereoisomers is likely to be optically active? 2R,3R 2S,3S 2R,3R 2S,3S

(d) Is any of the stereoisomers a meso isomer?

yes, 2R,3S, since it fits the definition of a meso isomer: it has chirality centres but also a plane of symmetry
(ie it is not chiral)

16. Why is it useful to be able to recognise chirality centress in a molecule?

when there are one or more chirality centres, stereoisomers exist
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revision of interparticle forces and physical properties

1. Which of the the following molecules can form hydrogen bonds among themselves? Draw a
diagram to show the hydrogen bonding. How does this type of hydrogen bond formation affect
physical properties? diethyl ether, butylamine (CH3CH2CH2CH2NH2), butanal

Of these three, only butylamine can form H-bonds to itself

δ+
δ− H
H-bonding contributes to attraction between molecules, H
N N
causing the boiling point to be higher than it would be if H H
only London forces were acting.

2. Which of the the following molecules can form hydrogen bonds with water? Draw a diagram to
show the hydrogen bonding. How does this type of hydrogen bond formation affect physical
properties? diethyl ether, butylamine (CH3CH2CH2CH2NH2), butanal

Each of these three can form H-bonds to water.

All that is needed for this is the NEGATIVE end of a hydrogen bond (a lone pair on O or N).
H-bonding results in attraction to water molecules, causing the solubility in water to increase.

δ+ δ+ δ+
δ−
H δ− H δ− H
H
O O δ− δ+
N O O
H N H
H H O
H H
H

3. Without referring to data tables, arrange the following sets of compounds in order of increasing
water solubility. Give your reasons.
a) 1-hexanol, 1-octanol, 1-butanol
b) 1-butanol, butane, 1,4-butanediol
c) diethyl ether, 1,2-dimethoxyethane, pentane

a) 1-octanol < 1-hexanol < 1-butanol; same H-bonding, but decreasing carbon chain length.

b) butane < 1-butanol < 1,4-butanediol; same number of carbons, but increasing number of
oxygens results in increasing amount of H-bonding to water.
1-Butanol is 10% soluble, 1,4-butanediol 100%

c) pentane < diethyl ether CH3CH2OCH2CH3 < 1,2-dimethoxyethane CH3OCH2CH2OCH3 ;

the last two differ only in the number of ether oxygens (H-bonding to water), pentane has
no H-bonding at all. [Diethyl ether is about 10% soluble in water,
while 1,2-dimethoxyethane is 100% (ie mixes with water in all proportions).]

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4. Without referring to data tables, arrange the following sets of compounds in order of increasing
boiling point. Give your reasons.
a) 1-hexanol, 1-octanol, 1-butanol
b) 1-butanol, butane, 1,4-butanediol
c) diethyl ether, dimethyl ether, 1-butanol

a) 1-butanol < 1-hexanol < 1-octanol; same amount of H-bonding, but increasing size of
carbon chain leads to increasing strength of London forces contributing to the attraction
between the molecules.

b) butane < 1-butanol < 1,4-butanediol; same number of carbons, but increasing number of
oxygens results in increasing amount of H-bonding between the molecules, as well as
increasing London forces:
butane is a gas, 1-butanol boils at 118°, 1,4-butanediol boils above 250°

c) dimethyl ether CH3OCH3 < diethyl ether CH3CH2OCH2CH3 < 1-butanol

the ethers have no H-bonding, so the only difference is their London forces;
diethyl ether and 1-butanol are isomers ∴ have similar London forces, but 1-butanol has
H-bonding while diethyl ether does not.

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