Transcript Slide 1

Organic Chemistry
6th Edition
Chapter 2
Paula Yurkanis Bruice
An Introduction to
Organic Compounds
Nomenclature,
Physical Properties,
and
Representation of
Structure
1
© 2011 Pearson Education, Inc.
Alkanes are hydrocarbons containing only single bonds
General formula: CnH2n+2
2
© 2011 Pearson Education, Inc.
3
© 2011 Pearson Education, Inc.
Constitutional isomers have the same molecular formula,
but their atoms are linked differently
4
© 2011 Pearson Education, Inc.
Nomenclature of Alkyl Substituents
Removing a hydrogen from an alkane results in an alkyl
substituent
5
© 2011 Pearson Education, Inc.
If a hydrogen is replaced by an OH, the compound
becomes an alcohol;
if it is replaced by an NH2, the compound becomes an
amine;
6
© 2011 Pearson Education, Inc.
if it is replaced by a halogen, the compound becomes an
alkyl halide;
and if it is replaced by an OR, the compound becomes an
ether
Some common names are derived from the alkyl groups
7
© 2011 Pearson Education, Inc.
Different Kinds of Carbons and
Hydrogens
8
© 2011 Pearson Education, Inc.
A compound can have more than one name, but a
name must specify only one compound
The prefix “tert” is used for tert-butyl and tert-pentyl
compounds
9
© 2011 Pearson Education, Inc.
The use of an “iso” prefix:
10
© 2011 Pearson Education, Inc.
11
© 2011 Pearson Education, Inc.
Nomenclature of Alkanes
1. Determine the number of carbons in the longest continuous
chain
12
© 2011 Pearson Education, Inc.
2. Number the chain so that the substituent gets the lowest
number
13
© 2011 Pearson Education, Inc.
Numbers are used only for systematic names but not
common names
14
© 2011 Pearson Education, Inc.
3. Number the substituents to yield the lowest possible number
in the number of the compound
substituents are listed in
alphabetical order
15
© 2011 Pearson Education, Inc.
4. Assign the lowest possible numbers to all of the substituents
16
© 2011 Pearson Education, Inc.
5. If the same substituent numbers are obtained in both directions,
the first group cited receives the lower number
6. If a compound has two or more chains of the same length, the
parent hydrocarbon is the chain with the greatest number of
substituents
17
© 2011 Pearson Education, Inc.
7. Certain common nomenclatures are used in the IUPAC system
Some substituents have only a systematic name
18
© 2011 Pearson Education, Inc.
Systematic Naming of Substituents
Systematic Method
•Determine longest chain starting with the point of attachment.
•Name longest chain as “alkyl.”
•Number and name substituents and add to “alkyl” as prefix.
•Name the substituent as (#-alkylalkyl). The parentheses distinguish
substituent numbering from the numbering of the longest chain.
19
© 2011 Pearson Education, Inc.
Nomenclature of Cycloalkanes
1. No number is needed for a single substituent on a ring
2. Name the two substituents in alphabetical order
20
© 2011 Pearson Education, Inc.
3. If there are more than two substituents, they are cited in
alphabetical order
21
© 2011 Pearson Education, Inc.
Nomenclature of Alkyl Halides
In the IUPAC system, alkyl halides are named as substituted
alkanes
22
© 2011 Pearson Education, Inc.
Nomenclature of Ethers
As substituents:
23
© 2011 Pearson Education, Inc.
Nomenclature of Alcohols
• In an alcohol, the OH is a functional group
• A functional group is the center of reactivity in a
molecule
24
© 2011 Pearson Education, Inc.
1. Determine the longest hydrocarbon containing the functional
group:
2. The functional group suffix should get the lowest number:
25
© 2011 Pearson Education, Inc.
3. When there is both a functional group suffix and a substituent,
the functional group suffix gets the lowest number:
4. The chain is numbered in the direction that gives a substituent
the lowest number:
26
© 2011 Pearson Education, Inc.
5. The functional group substituent on a ring gets the number 1,
but the functional group is not numbered in the name:
CH3
HO
CH3
OH
CH3
CH3
OH
3-methylcyclohexanol
not
3-methylcyclohexan-1-ol
1-methylcyclohexanol
not
1-methylcyclohexan-1-ol
2, 2-dimethylcyclopentanol
not
2, 2-dimethylcyclopentan-1-ol
6. If there is more than one substituent, the substituents are cited
in alphabetical order:
27
© 2011 Pearson Education, Inc.
Nomenclature of Amines
28
© 2011 Pearson Education, Inc.
The substituents are listed in alphabetical order and a number or
an “N” is assigned to each one:
29
© 2011 Pearson Education, Inc.
Naming Quaternary Ammonium Salts
A disinfectant and Antiseptic
30
© 2011 Pearson Education, Inc.
31
© 2011 Pearson Education, Inc.
Common Names Preferred over
Systematic Names in Some Cases
Pentacyclo[4.2.0.02,5.03,8.04,7]octane
“Cubane”
Nonacyclo[11.7.1.12,28.0 3,16.04,13.05,10.06,14.07,11.0 15,20] docosane
“Bastardane” The unwanted alkane.
32
© 2011 Pearson Education, Inc.
Structures of Alkyl Halides
33
© 2011 Pearson Education, Inc.
Structures of Alcohol and Ether
34
© 2011 Pearson Education, Inc.
Structures of Amines
35
© 2011 Pearson Education, Inc.
Attractive Forces
van der Waals force
Dipole–dipole interaction
Hydrogen bonds
The greater the attractive forces between molecules,
the higher is the boiling point of the compound.
36
© 2011 Pearson Education, Inc.
van der Waals Forces
The boiling point of a compound increases with the
increase in van der Waals force
© 2011 Pearson Education, Inc.
37
Dipole–Dipole Interaction
Dipole–dipole interactions are stronger than van der
Waals force but weaker than ionic or covalent bonds
38
© 2011 Pearson Education, Inc.
39
© 2011 Pearson Education, Inc.
Hydrogen bonds are stronger than other dipole-dipole
interactions and van der Waals force
40
© 2011 Pearson Education, Inc.
41
© 2011 Pearson Education, Inc.
Both van der Waals and dipole-dipole interactions must
be overcome for an alkyl halide to boil
42
© 2011 Pearson Education, Inc.
The melting point is influenced by the packing of the
molecules in the crystal lattice
43
© 2011 Pearson Education, Inc.
Like Dissolves Like
• Polar compound dissolves in polar solvent
• Nonpolar compound dissolves in nonpolar solvent
44
© 2011 Pearson Education, Inc.
“Like Dissolves Like” Concept Important in
Drug Action
• Crossing the Blood-Brain Barrier requires a fat-soluble drug.
• THC and Barbiturates possess hydrocarbon tails to facilitate
crossing this barrier.
• Hydrocarbon substituents are termed “lipophilic” or fat-loving.
• Substituents that possess hydrogen-bonding capability are
termed “hydrophilic”or water-loving.
45
© 2011 Pearson Education, Inc.
Conformations of Alkanes:
Rotation about Carbon–Carbon Bonds
46
© 2011 Pearson Education, Inc.
Different Conformations of Ethane
47
© 2011 Pearson Education, Inc.
A staggered conformer is more stable than an eclipsed
conformer
48
© 2011 Pearson Education, Inc.
Conformations of n-Butane
49
© 2011 Pearson Education, Inc.
Steric strain: repulsion between the electron clouds of atoms or
groups
The gauche interaction destabilizes the gauche conformation 50
© 2011 Pearson Education, Inc.
Cycloalkanes: Ring Strain
• Angle strain results when bond angles deviate from the
ideal 109.5° bond angle
51
© 2011 Pearson Education, Inc.
The chair conformation of cyclohexane is free of strain
52
© 2011 Pearson Education, Inc.
Ring Flipping in Cyclohexane
53
© 2011 Pearson Education, Inc.
Drawing Cyclohexane
54
© 2011 Pearson Education, Inc.
The Conformations of Cyclohexane
and Their Energies
55
© 2011 Pearson Education, Inc.
Conformations of Monosubstituted
Cyclohexanes
56
© 2011 Pearson Education, Inc.
57
© 2011 Pearson Education, Inc.
Steric Strain of 1,3-Diaxial Interaction in
Methylcyclohexane
58
© 2011 Pearson Education, Inc.
The larger the substituent on a cyclohexane ring, the
more the equatorial substituted conformer will be
favored
Keq = [equatorial conformer]/[axial conformer]
© 2011 Pearson Education, Inc.
59
The Chair Conformers of cis- or trans1,4-Dimethylcyclohexane
60
© 2011 Pearson Education, Inc.
Systematic Method for Drawing Chair
Conformations of Cis and Trans Substituted
Cyclohexanes
1. Label the chair conformer axial and equatorial bonds
with either up (U) or down (D) based on the flat
cyclohexane ring.
2. Consider Cis substituents as either UU or DD and Trans
substituents as either UD or DU.
3. Example, Draw the more stable conformation of cis-1,3dimethylcyclohexane:
61
© 2011 Pearson Education, Inc.
62
© 2011 Pearson Education, Inc.
63
© 2011 Pearson Education, Inc.
1-tert-Butyl-3-Methylcyclohexane
64
© 2011 Pearson Education, Inc.
Conformations and Drug Action
Etorphine, a rigid morphine analog:
65
© 2011 Pearson Education, Inc.
Conformations and Drug Action
• Conformations of the neurotransmitter dopamine
• Apomorphine natural products: conformationally-restricted
forms of dopamine:
•Apomorphine, active dopamine mimic; Isoapomorphine, inactive
66
as dopamine mimic
© 2011 Pearson Education, Inc.