New chm 152_unit_11_power_points-su13

ORGANIC CHEMISTRY I

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15-1

HYDROCARBONS
NOMENCLATURE
REACTIONS
Chapter 23 (McM)
Chapter 15.1-15.2 Silberberg

Chapter 15

Organic Compounds and the
Atomic Properties of Carbon

15-2

Organic Compounds and the Atomic Properties of Carbon
15.1 The Special Nature of Carbon and the Characteristics of
Organic Molecules

15.2 The Structures and Classes of Hydrocarbons

15-3

Goals & Objectives
• See the Learning Objectives on
page 618.
• Understand these Concepts:
• 15.1-6.
• Master these Skills:
• 15.1-2.
15-4

Organic Chemistry
• study of the compounds of carbon

15-5

Bonding Properties of Carbon
• Carbon forms covalent bonds in all its elemental forms
and compounds.
– The ground state electron configuration of C is [He]2s22p2; the
formation of carbon ions is therefore energetically unfavorable.
– C has an electronegativity of 2.5, which is midway between that
of most metals and nonmetals. C prefers to share electrons.

• Carbon exhibits catenation, the ability to bond to itself
and form stable chain, ring, and branched compounds.
– The small size of the C atom allows it to form short, strong
bonds.

– The tetrahedral shape of the C atom allows catenation.

15-6

Figure 15.1

15-7

The position of carbon in the periodic table.

Comparison of Carbon and Silicon
• As atomic size increases down the group, bonds
between identical atoms become longer and weaker.
– A C–C bond is much stronger than a Si–Si bond.

• The bond energies of a C–C bond, a C–O bond, and a
C–Cl bond are very similar.
– C compounds can undergo a variety of reactions and remain
stable, while Si compounds cannot.

• Si has low energy d orbitals available for reaction,
allowing Si compounds to be more reactive than C
compounds.

15-8

Diversity and Reactivity of Organic Molecules
• Many organic compounds contain heteroatoms, atoms
other than C and H.
– The most common of these are O, N, and the halogens.

• Most reactions involve the interaction of electron rich
area in one molecule with an electron poor site in
another.
– C–C bonds and C–H bonds tend to be unreactive.
– Bonds between C and a heteroatom are usually polar, creating
an imbalance in electron density and providing a site for
reactions to occur.

15-9

Hydrocarbons
• contain only carbon and hydrogen
• Saturated--contain the maximum
amount of hydrogen--contain only
single bonds
• Unsaturated--do not contain the
maximum amount of hydrogen-contain double and/or triple bonds

15-10

Hydrocarbons
• Cyclic compounds--contain rings in
the structure
• Aromatic compounds--includes
benzene and its derivatives--special
class of compounds

15-11

Drawing Carbon Skeletons
Each C atom can form a maximum of four bonds.
These may be four single bonds, OR one double and two single bonds,
OR one triple and one single bond.

The arrangement of C atoms determines the skeleton, so a
straight chain and a bent chain represent the same
skeleton.
Groups joined by a single bond can rotate freely, so a
branch pointing down is the same as one point up.

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Figure 15.4 Adding the H-atom skin to the C-atom skeleton.

A C atom single-bonded to one
other atom gets three H atoms.

A C atom single-bonded to three
other atoms gets one H atom.

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A C atom single-bonded to two
other atoms gets two H atoms.

A C atom single-bonded to four other atoms
is already fully bonded (no H atoms).

Figure 15.4 continued

A double-bonded C atom is
treated as if it were bonded to
two other atoms.
A double- and single-bonded C
atom or a triple-bonded C atom is
treated as if it were bonded to three
other atoms.

15-14

Sample Problem 15.1

Drawing Hydrocarbons

PROBLEM: Draw structures that have different atom arrangements
for hydrocarbons with
(a) Six C atoms, no multiple bonds, and no rings
(b) Four C atoms, one double bond, and no rings
(c) Four C atoms, no multiple bonds, and one ring
PLAN: In each case, we draw the longest carbon chain first and
then work down to smaller chains with branches at
different points along them. Then we add H atoms to give
each C a total of four bonds.

15-15

Sample Problem 15.1
(a) Six carbons, no rings

15-16

Sample Problem 15.1
(b) Four C atoms, one double bond, and no rings

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Sample Problem 15.1
(c) Compounds with four C atoms and one ring

15-18

Alkanes
Hydrocarbons contain only C and H.
Alkanes are hydrocarbons that contain only single bonds
and are referred to as saturated hydrocarbons.
The general formula for an alkane is CnH2n+2, where n is
any positive integer.
Alkanes comprise a homologous series, a group of
compounds in which each member differs from the next by
a –CH2– group.

15-19

Alkanes
• simplest saturated hydrocarbons
• general formula CnH2n+2
• first member of the alkane series is
methane, CH4

15-21

Naming Organic Compounds
The name of any organic compound is comprised of three
portions:
PREFIX + ROOT + SUFFIX
The root name of the compound is determined from the
number of C atoms in the longest continuous chain.

The suffix indicates the type of organic compound, and is
placed after the root.
The suffix for an alkane is –ane.

The prefix identifies any groups attached to the main
chain.

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Table 15.1

Numerical Roots for Carbon Chains and Branches
Roots
meth-

1

eth-

2

prop-

3

but-

4

pent-

5

hex-

6

hept-

7

oct-

8

non-

9

dec-

15-23

Number of C
Atoms

10

Figure 15.5

15-24

Ways of depicting the alkane 3-ethyl2-methylhexane.

Isomers


15-25

compounds having the same molecular
formula but with different structural
formulas

Constitutional Isomers
Constitutional or structural isomers have the same
molecular formula but a different arrangement of the
bonded atoms.
A straight-chain alkane may have many branched
structural isomers.
Structural isomers are different compounds and have
different properties.
If the isomers contain the same functional groups, their properties
will still be similar.

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Table 15.3

15-29

The Constitutional Isomers of C4H10 and C5H12

Figure 15.7

Formulas, molar masses (in g/mol), structures, and
boiling points (at 1 atm pressure) of the first 10
unbranched alkanes.

Alkanes are nonpolar and their physical properties are
determined by the dispersion forces between their molecules.

15-30

Isomers
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•
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•

15-31

C7H16 -- 9 isomers
C10H22 -- 75 isomers
C15H32 -- 4,347 isomers
C30H62 -- 4,111,846,763 isomers

Nomenclature of Alkanes
• Name the following compound using
the IUPAC system of nomenclature.
• CH3CH2CHCH3
•
CH3

15-32

• 1. Choose the longest chain of
carbon atoms in the structure and
give that chain the name of the
member of the alkane series having
the same number of carbon atoms.
– butane

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• 2. Number the C atoms in that
longest chain starting at the end that
will give the smallest number at the
substituted position.

• 3. Precede the parent name with the
position number and name of each
substituting group.

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• CH3CH2CHCH3
•
CH3
• 2-methylbutane

15-36

• 4. Separate numbers from numbers
with commas and numbers from
words with hyphens.

15-37

• Give IUPAC names for each of the
following compounds
• Draw the isomers and give the
IUPAC name of the possible isomers
of C6H14

15-38

Alkenes
A hydrocarbon that contains at least one C=C bond is
called an alkene.
Alkenes are unsaturated and have the general formula
CnH2n.

To name an alkene, the root name is determined by the
number of C atoms in the longest chain that also
contains the double bond.
The C chain is numbered from the end closest to the double bond.
The suffix for alkenes is –ene.

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Unsaturated Hydrocarbons
• 1. Alkenes, CnH2n
– contain C=C
– CH2=CH2
ethene
– CH3CH=CH2 propene
– CH3CH2CH=CH2 1-butene
– CH3CH=CHCH3 2-butene

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Geometric Isomers
The double bond of an alkene restricts rotation, so that
the relative positions of the atoms attached to the double
bond are fixed.
Alkenes may exist as geometric or cis-trans isomers,
which differ in the orientation of the groups attached to
the double bond.
Geometric isomers have different physical properties.

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Table 15.4

15-46

The Geometric Isomers of 2-Butene

Alkynes
An alkyne is a hydrocarbon that contains at least one
CΞC triple bond.
Alkynes have the general formula CnH2n-2 and they are
also considred unsaturated carbons.

Alkynes are named in the same way as alkenes, using
the suffix –yne.

15-47

Unsaturated Hydrocarbons
• 2. Alkynes, CnH2n-2
– contain carbon-carbon triple bonds
– C2H2
– C3H4
– C4H6

15-48

Sample Problem 15.2

Naming Alkanes, Alkenes, and Alkynes

PROBLEM: Give the systematic name for each of the following,
indicate the chiral center in part (d), and draw two
geometric isomers for part (e).

PLAN: For (a) to (c), we find the longest continuous chain (root) and
add the suffix –ane because there are only single bonds. Then
we name the branches, numbering the C chain from the end
closest to the first branch. For (d) and (e) the longest chain must
include the double bond.

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Sample Problem 15.2
SOLUTION:

2,3-dimethylbutane
3,4-dimethylhexane

1-ethyl-2-methylcyclopentane

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Sample Problem 15.2

3-methyl-1-pentene

cis-2,3-dimethyl-3-hexene

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trans-2,3-dimethyl-3-hexene

• Give IUPAC names for each of the
following compounds
• Draw the isomers and give the
IUPAC name of the possible isomers
of C5H12

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Cyclic Hydrocarbons –
CnH2n

15-58

Figure
15.6

Depicting cycloalkanes
H

H

H

15-59

C H

H C

C H

C H

H

H

cyclobutane
cyclopropane

H

H C

C
H C

H

H

Figure
15.6

Depicting cycloalkanes
H
H
H
H C
H

cyclopentane

15-60

H

C
C

H

H
C
C
H

H
H

cyclohexane

H

H

H C
H C

C

H

C H
C H
C
H
H
H H

Figure 15.13

Representations of benzene.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Resonance forms
having alternating single
and double bonds.

Resonance hybrid shows the
delocalized electrons as either
an unbroken or a dashed circle.

Benzene is an aromatic hydrocarbon.
15-62

methylbenzene
(toluene)
bp = 110.6 C

1,2-dimethylbenzene
(o-xylene)
bp = 144.4 C

1,4-dimethylbenzene
(p-xylene)
bp = 138.3 C

15-63

1,3-dimethylbenzene
(m-xylene)
bp = 139.1 C

2,4,6-trinitromethylbenzene
(trinitrotoluene, TNT)

Tools of the Laboratory Nuclear Magnetic Resonance (NMR)
Spectroscopy

Figure B15.1

15-64

The basis of proton spin resonance.

Spectroscopy
Figure B15.2

15-65

The 1H-NMR spectrum of acetone.

Spectroscopy
Figure B15.3

15-66

The 1H-NMR spectrum of dimethoxymethane.

Spectroscopy
Figure B15.4

15-67

An MRI scan showing a brain tumor.

Dr . Kay Sandberg’s Nomenclature
Presentation from NC State
• The presentation can be reached at
the following link:
• http://courses.ncsu.edu/ch221/comm
on/kas/Alkane_Nomenclature/Alkane
-Nomenclature.html

15-68

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