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Chapter 25 – Organic Chemistry
Reading: sections 25.1 – 25.5 in 11th edition, sections 25.1-25.7 (in 10th edition)
As you read this material ask yourself the following questions:What is unique about carbon and carbon-based compounds? Why did life evolve around carbon?
Why does silicon not exhibit the great diversity if compounds that we find for carbon?
What are the main classifications of hydrocarbons?
How do the properties of structural isomers differ from one another?What is the difference between saturated and unsaturated hydrocarbons?
What is geometric isomerism in alkenes.
Chem 101 1
What kinds of reactions are common in alkenes and aromatics?
What are functional groups? Why are they important?
What are optical isomers or enantiomers? What sort of organicmolecules display this isomerism?
Organic chemistry, Chapter 25, sections 25.1- 25.5
The end to vitalism: living things have a vital force making it possible for them to form organic compounds
F. Wohler 1828
C
NH2
NH2 O
F. Wohler 1828
most odorants are organic compounds
Chem 101 2
organic chemistry: study of compounds containing C in combination with one or more other elements
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Carbon is unique
tendency to form four covalent bonds
ability to form double and triple bonds
forms strong covalent bonds
Chem 101 3
reactivity resides in– regions of high electron density, like C-O-H or C=O
carbon is unique, continued
tendency to catenate
solubility
water solubility is conferred by
Chem 101 4
water solubility is conferred by
acidic groups
basic groups
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Hydrocarbons
four different types:
Chem 101 5
largest possible no. of H atoms
Drawing hydrocarbon structures
Chem 101 6
butane and isobutane
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Alkanes - general formula:
structures based on
Lewis structure and condensed formula do not tell 3D structure
Free rotation about single bonds give alkanesmany shapes
molecular formulas are the same
C C C C C C C
C
is the same as
Chem 101 7
systematic names are required – IUPAC rules
Alkane nomenclature
1. Find the longest continuous chain of carbon atoms. This longest chain may not be written in a straight line.
2. Name that longest chain with the appropriate alkane name.
6 Precede each group name with a prefix indicating how many of them are
3. Find the substituents and name each of them with the appropriate group name.
4. Number the carbons in the chain such that the lowest number is given to the group nearest one end of the chain.
5. List the groups alphabetically in front of the longest chain name.
Chem 101 8
6. Precede each group name with a prefix indicating how many of them are present in the molecule. In front of the prefix, list the numbers of each group in the molecule and separate the numbers with a hyphen.
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other substituents
halogens
CH3CH2CH2CHCH2CHCH2CH3| |
CH3 CH3
-F
-Cl
-Br
-I
-OH
C CH3H3C
CH3
CH3
Chem 101 11
O
-NO2 write the structural formula for 3-chloro-2,4-dimethylpentane
Cycloalkanes - general formula:
carbon chains can form rings or cycles
well known and found in nature
CH2 CH2
CH2
Chem 101 12
rings with fewer than 5 carbon atoms are strained
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cycloalkane nomenclature
1. add cyclo to parent name
2. start numbering at the substituent group with alphabetical priority
3. number around ring so that substituents have lowest possible numbers
CH3
Br
CH3
Br
1
CH3
Br12
Chem 101 13
BrCH3
Br1
CH3
Br1
2
Reactions of alkanes
alkanes
combustion is important
methane and ethane
propane and butane – components in LPG (Liquefied petroleum gas)
also high mol. weight compounds: gasoline, oil, tar sands
Chem 101 14
all alkanes have the same combustion reaction:
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Chapter 25 – Organic Chemistry – PART 2
Reading: sections 25.1-25.3 ( to p. 1062 in11th edition), sections 25.1-25.3 (complete, in 10th edition)
As you read this material ask yourself the following questions:
Explain geometric isomerism in alkenes.
What kinds of reactions are common in alkenes and aromatics?
What are functional groups? Why are they important?
What are optical isomers or enantiomers? What sort of organicmolecules display this isomerism?
Chem 101 15
molecules display this isomerism?
Alkenes - general formula:
structures based on
at least two C atoms have
Chem 101 16
unsaturated hydrocarbon -
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geometry of alkenes
geometry constrained
t i i
Chem 101 17
geometric isomers
Nomenclature of alkenes
1. suffix is
2. parent = p
4. number the chain
3. position of double bond
Chem 101 18
5. proceed as for alkanes
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examples
Chem 101 19
alkene nomenclature cont’d…
geometric isomers ( if known) have to indicated in name
Chem 101 20
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16 6
cis and trans isomers can differ
4
6
1
5
2
3
4
6
3
5
2
Chem 101 21
1
4
6
52
3
4
6
5
1
3 3
2
Chem 101 22
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Reactions of alkenes
addition reactions
general reaction:
Br2, Cl2
Chem 101 23
Cl2
H2
addition rxns, cont’d
H2H2
H2O
H2OH2O
Chem 101 24
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addition rxns, cont’d
HBr
HBrHBrHBrHBr
Chem 101 25
omit mechanism of addition reactions topic, pp. 1066 – 1068 (11th
edition), pp. 1079 – 1080 10th edition
Alkynes - general formula:
unsaturated
Chem 101 26
addition reactions
2 H2
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Nomenclature of alkynes
1. suffix is
2. parent = p
4. number the chain
3. position of triple bond
Chem 101 27
5. proceed as for alkanes
Aromatic hydrocarbons
contain a 6-membered ring with 3 double bonds
chemically unlike alkenes and alkynes
resonance structures
Chem 101 28
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aromatic nomenclature
(only need to know the compounds in the text)
parentparent
naphthalene
prefix
B
Chem 101 29
CH3
Br
number
Br
Br
nomenclature, cont’d
Br
1, 2-dibromobenzene
Br
Br
Br 1, 3-dibromobenzene
Chem 101 30
1, 4-dichlorobenzene
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Reactions of aromatics
substitution reactions
in general:
Chem 101 31
HNO3
substitution rxns, cont’d
Br2
HNO3
Chem 101 32
HNO3
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Summary of hydrocarbon reactions
CnH2n+2 O2 CO2 H2OCnH2n+2 O2 CO2 H2O
XY
Chem 101 33
XY HY
Functional groups
group of atoms attached to hydrocarbon
two examples already reviewed:
most reactions involve regions of high electron density
Chem 101 34
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other common functional groups
Chem 101 35
Alcohols
related to water and to alkanes
Chem 101 36
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properties of alcohols
weakly acidic
Chem 101 37
H2O H3O+CH3O_
alcohol, preparation
methanol, called wood alcohol, prepared from CO and H2 in gas phase
ethanol – oldest known pure organic chemical, fermentation of sugar/ starch
Chem 101 38
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alcohol, preparation, cont’d
from alkenes, addition reaction
common alcohols:
ethylene glycol1 2 ethanediol
Chem 101 39
phenol
1,2-ethanediol
glycerol1,2,3-propanetriol
Ethers (R-O-R’) CH2
OCH
3
CH2 CH
3
formed by the reaction between two alcohols
R1-O-H + H-O-R2
flammable – only slightly polar -
will oxidize in air to form
Chem 101 40
used as anesthetics
or CF3CHCl-O-CF3 isoflurane
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Amines (R-NH2)
less polar than alcohols
Chem 101 41
reacts with acid to form salts
amines, cont’d
Used in the manufacture of dyes
indigo
drugs are amines and amino group important functional group for amino acids, peptides and proteins
Chem 101 42
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Functional groups with a C=O group
Chem 101 43
Aldehydes and Ketones
R
O
R 1 R
O
H
&
C atom has 3 electron domainsC atom has 3 electron domains
classified by the number of C atoms attached to carbonyl carbon atom
aldehyde
Chem 101 44
ketone no H atoms attached
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aldehyde and ketone cont’d
Chem 101 45
aldehydes and ketones, cont’d
many occur naturally
CHOH
ketones – solvents and perfumes
ld h d fl
HC
O
O
CH3
CH3aldehydes - flavours
Chem 101 46
CH
O
O
H3CCH3
H3C
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Carboxylic acids
occur widely in nature
Chem 101 47
H3C COOH
ethanoic acid or acetic acidquinic acid
carboxylic acids, cont’d…
behave as weak acids -
R COOH + H2O
can be neutralized by strong base
R COOH + NaOH
produced by oxidation of alcohols
CH3CH2CH2OH + [O]
Chem 101 48
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Esters
alkyl derivatives of carboxylic acids
Chem 101 49
formed by condensation reaction between alcohols and carboxylic acids
examples
CH3CH2C
O
OH HO-CH2CH2CH3+
H+ catalyst
Chem 101 50
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ester reaction
saponificationp
CH3CH2C
O
+ H2OO[OH-]
CH3
Chem 101 51
ester + water [OH-]
AmidesR
C N
O
H
resonance important:p
Chem 101 52
key functional group in peptides and proteins
formation of amide linkage is the important step in protein synthesis
A1AC N
O
H
AA2
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amides, cont’d
neutral – does not accept H+ or form ammonium-like salts
prepared by reaction of carboxylic acid with ammonia or amine
Chem 101 53
amides undergo hydrolysis
RC N
O
R1
R2+ H2O
H+
heat
Isomers
Isomers
structural isomers stereoisomers
Chem 101 54
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Optical isomers
Chem 101 55
to have optical isomers need:
molecule that has optical isomers
molecules that are optical isomers
Chem 101 56