Chapter 10 of General, Organic, and Biochemistry, Denniston, 7th edition

1. Chapter 10
An Introduction to Organic Chemistry
1

2. 10.1 The chemistry of carbon
Why are there so many carbon-based compounds?
Carbon atoms form stable, covalent bonds with each other.
Carbon atoms form stable bonds with other elements, such as
oxygen, nitrogen, sulfur, and halogens.
Carbon atoms form multiple bonds with:
other carbon atoms (double & triple);
oxygen (double);
nitrogen (double & triple).
Carbon atoms can be arranged in linear chains, branched
chains, and cyclic structures.
2

3. 10.1 Organic/inorganic compound differences
• Bond type
– Organics have covalent bonds
• Electron sharing
– Inorganics usually have ionic bonds
• Electron transfer
• Structure
– Organics
• Molecules
• Nonelectrolytes
– Inorganics
• Three-dimensional crystal structures
• Often water-soluble, dissociating into ions -electrolytes
3

4. 10.1 Organic/inorganic compound differences
• Melting point & boiling point
– Organics have covalent bonds
• Intermolecular forces broken fairly easily
– Inorganics usually have ionic bonds
• Ionic bonds require more energy to break
• Water solubility
– Organics
• Nonpolar, water insoluble
– Inorganics
• Water-soluble, readily dissociate
4

5. 10.1 Functional groups
Groups of atoms that cause organic compounds to
exhibit particular properties are called functional groups.
e.g., alcohols always have an –OH group.
We’ll be studying organic chemistry by functional group.
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6. 10.1 Functional groups
Alkenes contain a
double bond between
adjacent carbon
atoms.
Alkynes contain a
triple bond.
6

7. 10.1 Functional groups
An alcohol contains the
hydroxyl (-OH) functional
group.
In an ether, an oxygen atom
is bonded to two carbon
atoms.
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8. 10.1 Functional groups
An aldehyde contains a
carbonyl group (C=O), which is
a carbon atom with a double
bond to an oxygen atom.
In a ketone, the carbon of the
carbonyl group is attached to
two other carbon atoms.
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9. 10.1 Functional groups
Carboxylic acids contain the
carboxyl group, which is a
carbonyl group attached to
a hydroxyl group.
An ester contains the
carboxyl group between
carbon atoms.
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10. 10.1 Functional groups
In amines, the
functional group is a
nitrogen atom.
In amides, the hydroxyl
group of a carboxylic
acid is replaced by a
nitrogen group.
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11. 10.2 Alkanes
Hydrocarbons are compounds composed only of carbon
and hydrogen.
Saturated hydrocarbons have only single bonds.
Unsaturated hydrocarbons have one or more double and/or
triple bonds.
Saturated hydrocarbons are called
alkanes if they are acyclic.
cycloalkanes if they are cyclic.
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12. 10.2 Sources of alkanes
Petroleum, a naturally occurring mixture of
hydrocarbons, is the main source of alkanes.
Liquid petroleum is called crude oil.
hydrocarbons with 5 or more carbons
Gaseous petroleum is called natural gas.
mostly methane, with ethane, propane, and butane
12

13. 10.2 Sources of alkanes
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14. 10.2 Physical properties of alkanes
Alkanes are insoluble in water.
Water molecules are polar and can take part in hydrogen
bonding.
Alkanes are nonpolar.
“Like dissolves like.”
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15. 10.2 Physical properties of alkanes
Alkanes have lower boiling points for a given molecular
weight than most other organic compounds.
Alkanes are nonpolar.
Molecules are only weakly held together by van der Waals
attractions.
Because the attractions are weak, less energy is needed to
separate molecules from each other into the gas phase.
Therefore, boiling points are lower.
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16. 10.2 Physical properties of alkanes
The boiling points of alkanes rise as the chain length
increases and fall as the chains become branched and
more nearly spherical.
16

17. 10.2 Physical properties of alkanes
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18. 10.2 Physical properties of alkanes
This is a good place to answer your first Journal question
for this module.
[Use tag “water”]
Table salt (NaCl) dissolves in water, but iodine (I2) does
not to any appreciable extent. Explain why this is, in
terms of the molecular properties of salt, water, and
iodine.
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19. 10.2 Writing structural formulas
Some definitions:
Atoms bonded in a “straight” line are in a continuous chain.
A branched chain has some carbons branching off the longest
continuous chain.
19

20. 10.2 Writing structural formulas
Some hints:
First, attach the carbon atoms to each other in the correct
configuration.
Add hydrogen atoms until each carbon atom has four bonds.
Structural formula of C3H8
pencast
20

21. 10.2 Abbreviated structural formulas
Writing out every atom and bond individually is
inconvenient.
Abbreviated structural formulas list each carbon with its
hydrogens, adjacent to other carbons it is bonded to.
ethanol and dimethyl ether pencast
n-pentane, 2,2-dimethylpropane
pencast
21

22. 10.2 Abbreviated structural formulas
Line structures
use no element symbols.
show only carbon-carbon bonds.
Line structures for
n-pentane
2-methyl-butane
2,2-dimethylpropane
pencast
22

23. 10.2 Structures of alkanes
All alkanes fit the same general molecular formula.
CnH2n+2
where n = number of carbons
Normal alkanes (n-alkanes) have carbon chains that are
unbranched.
A group of alkanes that each has one more –CH2– group
is called a homologous series.
Properties of the molecules are similar.
Properties change gradually as carbon atoms are added.
23

24. 10.2 Structures of alkanes
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25. 10.2 Structures of alkanes
Which of the following are alkanes?
C7H18
C7H16
C8H16
C27H56
25

26. 10.2 Alkyl groups
An alkyl group is an alkane with one hydrogen atom
removed
It is named by replacing the -ane of the alkane name with
–yl
Methane becomes a methyl group.
CH4 – H = -CH3
Ethane becomes an ethyl group.
CH3CH3 – H = -CH2CH3
26

27. 10.2 Alkyl groups
27

28. 10.2 Alkyl groups
Alkyl groups are classified according to the number of
carbons attached to the carbon atom that joins the alkyl
group to a molecule.
A primary carbon (1o) is directly bonded to one other carbon.
A secondary carbon (2o) is directly bonded to two other
carbons.
A tertiary carbon (3o) is directly bonded to three other carbons.
A quaternary carbon (4o) is directly bonded to four other
carbons.
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29. 10.2 Alkyl groups
29

30. 10.2 Nomenclature
Organic compounds were initially named after their
source, use, and properties.
There are now over 15 million organic compounds
known!
Clearly, it is necessary to have a systematic method for
naming.
Every compound must have a unique name.
Structure must be determinable from the name.
The name must be determinable from the structure.
The system we use is called IUPAC.
It was devised by the International Union of Pure and Applied
Chemistry.
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31. 10.2 IUPAC rules for naming alkanes
The –ane ending is used for all alkanes.
Alkanes without branching are named by the number of
carbon atoms.
For branched alkanes, the root name is the one for the
longest continuous chain of carbon atoms.
Groups attached to the main chain are called
substituents.
Saturated groups composed of carbon and hydrogen are called
alkyl groups.
Alkyl groups are named after the corresponding alkane, with –yl
replacing –ane.
31

32. 10.2 IUPAC rules for naming alkanes
The main chain is numbered so the first substituent has
the lowest possible number.
All substituent names are preceded by the number of the
carbon they are attached to.
If there are two or more identical substituents, there are
two or more numbers preceding the name, and
a prefix (di-, tri-, tetra-, . . .) on the substituent name.
If two or more different substituents are present, they
are listed alphabetically (ignoring any number prefix).
The only punctuation used is
commas to separate numbers from each other.
hyphens to separate letters from numbers.
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33. 10.2 IUPAC rules for naming alkanes
Give the IUPAC names for the following compounds:
pencast
pencast
33

34. 10.2 Alkyl and halogen substituents
Alkyl groups are named by changing the –ane ending of
alkanes to –yl.
methyl CH3-
ethyl CH3CH2-
n-propyl CH3CH2CH2-
isopropyl (1-methylethyl) CH3CHCH3
butyl CH3CH2CH2CH2-
sec-butyl (1-methylpropyl) CH3CH2CH2CH2
isobutyl (2-methylpropyl) (CH3)2CHCH2-
tert-butyl (1,1-dimethylethyl) (CH3)3C-
34

35. 10.2 Alkyl and halogen substituents
Halogen substituents are named by changing the –ine
ending of the element to –o.
fluoro- F-
chloro- Cl-
bromo- Br-
iodo- I-
R is a general symbol for an alkyl group.
R-H is any alkane.
R-Cl or R-F or R-Br or R-I stand for alkyl halides.
35

36. 10.2 Alkyl and halogen substituents
Give a IUPAC name for CH2ClF.
Write a formula for each compound.
1,1,1,-trichlorodecane
pencast
3,3,5-trimethylpentane
Name the following compounds.
CH3CH2CH(CH2CH3)CH2CH2CH3 pencast
CH3C(CH3)2CH(CH2CH3)CH2CH2CH3
pencast
36

37. 10.2 Use of the IUPAC rules
2-methylpentane
(not 4-methylpentane)
3-methylhexane
(not 2-ethylpentane or
4-methylhexane)
2,2-dimethylbutane
(not 2,2-methylbutane or
2-dimethylbutane)
3-bromo-1-chlorobutane
(not 1-chloro-3-bromobutane or
2-bromo-4-chlorobutane)
37

38. 10.2 Isomerism
If more than one arrangement is possible for a given
molecular formula, the different arrangements are called
isomers.
Structural isomers have the same molecular formula but
different structural formulas.
Consider the molecular formula C3H7Cl.
isomer 1
isomer 2
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39. 10.2 Isomerism
There are 5 structural isomers of C6H14.
pencast
Draw the 5 isomers and name them.
39

40. 10.2 Isomerism
Although all 5 isomers have the same molecular
formula, their physical properties vary.
40

41. 10.2 Isomerism
How about another Journal question?
[Use tag “isomers”]
In this power point, you’ve seen data indicating that the
five isomers of C6H14 have different physical properties.
With reference to the slides on properties of alkanes,
explain the relative melting and boiling points of these
isomers. That is, look at the shapes of the molecules (the
amount of branching) and explain how the shapes
correlate with the melting and boiling points.
41

42. 10.3 Cycloalkanes
Cycloalkanes have two fewer hydrogens than the
corresponding chain alkane.
hexane, C6H14
cyclohexane, C6H12
The general formula for a cycloalkane is CnH2n.
42

43. 10.3 Cycloalkanes
To name cycloalkanes, add the prefix cyclo- to the name
of the corresponding alkane.
Place substituents in alphabetical order before the base
name as for alkanes.
For multiple substituents, use the lowest possible set of
numbers; a single substituent requires no number.
43

44. 10.3 Cycloalkanes
Cyclopropane
Cyclobutane
Cyclohexane
44

45. 10.3 Naming cycloalkanes
Name the two cycloalkanes shown.
Parent chain
6 carbon ring, cyclohexane
5 carbon ring, cyclopentane
Substituent
1 chlorine atom, chloro-
1 methyl group, methyl-
chlorocyclohexane
methylcyclopentane
45

46. 10.3 cis-trans isomers in cycloalkanes
Atoms of an alkane can rotate freely around the carbon-
carbon single bond having an unlimited number of
arrangements.
Rotation around the bonds in a cyclic structure is limited
by the fact that all carbons in the ring are interlocked.
Formation of cis-trans (geometric) isomers is a
consequence of the lack of free rotation around bonds.
Stereoisomers are molecules that have the same
structural formulas and bonding patterns, but different
arrangements of atoms in space. See “Videos with
Models” in “Powerpoints
and Related Materials”
folder for Module 1
46

47. 10.3 cis-trans isomers in cycloalkanes
Two groups may be on the same side (cis) of the imagined plane of
the cyclo-ring or they may be on the opposite side (trans).
Geometric isomers do not readily interconvert, because this would
involve bond breaking and re-formation.
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48. 10.3 Practice with cycloalkanes
Name the following compounds:
pencast
48

49. 10.3 Practice with cycloalkanes
Draw structures for the following compounds.
trans-1,4-dimethylcyclooctane
cis-1,3-dichlorocyclohexane pencast
cis-1-bromo-2-fluoro-cyclobutane
49

50. 10.4 Conformations of alkanes
Geometric isomers have the same number of atoms of
each type, but are bonded together differently.
Bonds must be broken to change one geometric isomer into
another.
Conformers are identical molecules that are arranged
differently in space (rotation around single bonds).
An intact molecule can be changed from one conformation to
another.
50

51. 10.4 Ethane and butane
In an eclipsed conformation, groups on the front and
back carbons are aligned when we look down the bond.
51

52. 10.4 Ethane and butane
In a staggered conformation, groups on the front and
back carbons are not aligned when we look down the
bond.
See “Videos with
Models” in “Powerpoints
and Related Materials”
folder for Module 1
52

53. 10.4 Journal
Last Journal question for this Module
[Use tag “butanes”]
Consider the molecules butane and cyclobutane.
If two substituents are added to cyclobutane, they can be cis- or
trans-. If two substituents are added to butane, these is no
possibility of cis- and trans- isomers;
however,
butane has conformers, and cyclobutane does not.
Explain these two observations in terms of the structures
of butane and cyclobutane, and the definitions of cis- and
trans- isomers and conformers.
53

54. 10.4 Cyclohexane
Because of the 109.5o carbon-
carbon bonds, a cyclohexane ring
doesn’t lie flat, but is puckered.
“Boat” conformation: both ends
puckered up.
“Chair” conformation: one end up,
one end down.
54

55. 10.4 Cyclohexane
The chair conformation of cyclohexane is more stable
than the boat conformation because the hydrogens are
less crowded.
55

56. 10.4 Cyclohexane
On each carbon in the
cyclohexane ring, one
hydrogen is vertical to a
plane through the ring. See “Videos with
Models” in
“Powerpoints
These are the axial and Related
Materials” folder
hydrogens. for Module 1
The second hydrogen on
each carbon is the
equatorial hydrogen.
56

57. 10.5 Reactions: Combustion
Alkanes and cycloalkanes react with oxygen to produce
carbon dioxide and water.
This is an oxidation reaction…
…but we usually call it combustion.
What’s wrong with this equation for the combustion of
methane?
CH4 + O2  CO2 + H2O
57

58. 10.5 Reactions: Combustion
Guidelines for balancing combustion reactions:
Balance carbon using CO2 product molecules.
Balance hydrogen using H2O product molecules.
Balance oxygen using O2 reactant molecules.
Write a balanced chemical equation for the combustion
of the following compounds:
pentane
cyclopropane
2-methylhexane
58

59. 10.5 Reactions: Halogenation
In a substitution reaction, one atom substitutes for
another on a molecule.
Halogenation is the replacement of a hydrogen on an
alkane with a halogen atom.
Since alkanes and cycloalkanes aren’t very reactive, heat
or light must be present for halogenation to take place.
59

60. 10.5 Reactions: Halogenation
Terminology: If one halogen is added per molecule:
monochlorination
monobromination
If all the hydrogens in the molecule are not equivalent, a
mixture of products will form.
3-D, rotatable model 3-D, rotatable model
1-chloropropane 2-chloropropane
What are all the possible monochlorination products of
pentane? pencast
60

61. 10.5 Reactions: Halogenation
If the halogenation reaction is allowed to continue, more
than one halogen may add to each molecule.
CH4 + ½ Cl2  CH3Cl + HCl
CH4 + Cl2  CH2Cl2 + 2 HCl
CH4 + 3/2 Cl2  CHCl3 + 3 HCl
CH4 + 2 Cl2  CCl4 + 4 HCl
61

62. End-of-chapter notes
Summary of reactions for the class of compounds studied in
the chapter
Know what reactions these compounds undergo.
Know what the reactants and products are.
Know what the conditions for reaction are.
Be able to write a balanced equation for each reaction.
Key terms
These should all be familiar to you by the time we finish the chapter.
Know definitions for these terms—you’ll need them in later chapters.
Summary for each section of the chapter
If you don’t understand everything in the chapter summaries, go back
and figure out what it means!
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