Transcript Organic Chemistry

Organic Chemistry
Chapter 25
Chemistry 100
Organic Chemistry
Historically: the chemistry of products
from plants and animals
 Today: The chemistry of carboncontaining compounds
 Wöhler (1828) made urea from
ammonium cyanate


Distinction between “natural” and “synthetic”
chemicals disappeared.
The world of plenty
The American Chemical Society has a
database with more than 11 million
organic compounds
 Why so many?
 Because carbon can make chains and
rings, and things

Carbon




Electronic configuration
1s22s22p2
Needs 4 electrons to
complete the shell
Electronegativity 2.5 so it
forms covalent bonds with
other elements
2s22p2 makes hybrid
orbitals sp3 - tetrahedron
Functional Groups
We look at an organic molecule and ask
“what functional groups does it have?
 Examples




Alcohols have the OH group
Amines have the NH2 group
Unsaturated compounds have double or triple
bonds C=C or CC
Functional groups



Acetic acid CH3COOH is a carboxylic acid - it
has the -COOH group
The compound CH3NH2 is methyl amine
An amino acid like glycine (see picture) has
both the carboxylate and the amino group
Categorizing organic compounds
There are so many we need a system to
name them
 Unlike biologists we use English words,
but sometimes you would not know this!

Hydrocarbons
contain only C and H

Aliphatic (meaning derived from fats)




Alkanes
Alkenes
Alkynes
CnH2n+2
CnH2n
CnH2n-2
Aromatic (yes - they smell)
contain one or more benzene rings
Alkanes CnH2n+2










n
n
n
n
n
n
n
n
n
n
=
=
=
=
=
=
=
=
=
=
1 Methane (marsh gas)
2 Ethane
3 Propane
4 Butane
5 Pentane (liquid)
6 Hexane
7 Heptane
8 Octane
9 Nonane
10 Decane
CH4
C 2 H6
C 3 H8
C4H10
C5H12
C6H14
C7H16
C8H18
C9H20
C10H22
Butane
Condensed formula
(two forms)
C4H10
CH3CH2CH2CH3
CH3(CH2)2CH3
H
H
H
H
H
C
C
C
C
H
H
H
H
H
Lewis structural
formula
Iso-butane
C4H10
CH3CH(CH3)CH3
We may think of this
as CH3CH2CH3 with
one of the H atoms
substituted by a CH3
group
CH3 CH CH3
CH3
H
H
H
H C
C
C
H
H
H C
H
H
A branched chain
H
Alkyl
groups
CH3Cl
methyl chloride
CH3CH2CH2OH
n-propyl alcohol
Naming larger alkanes
1
2
3
4
Find the longest continuous chain. Use this as
the base name
Number the C atoms, starting from the
nearest substitution
Name and give location of each substitued
group
When more than one group at the same
location:
use di, tri, tetra, penta if they are the same
name in alphabetical order, if different
Naming
Example
H2
C
H3C
H
C
CH
CH3
CH3
CH3
2,4-dimethylpentane
H3C
H2
C H
C
H2
C
C
H2
HC
H3C
CH3
H2
C
CH3
Petroleum products
Size
Fraction
Gas
C1 to C5
Boiling-Point Range
(0C)
-160 to 30
Gasoline
Kerosene, fuel-oil
C5 to C12
C12 to C18
30 to 200
180 to 400
Lubricants
Paraffins
Asphalt
C16 and up
C20 and up
C36 and up
350 and up
Low-melting solids
Gummy residues
Uses
Gaseous fuel,
production of H2
Motor fuel
Diesel fuel,
furnace fuel, cracking
Lubricants
Candles, matches
Surfacing roads
Cycloalkanes CnH2n
H2
C
H2C CH2
H2C
H2C
C
H2
H2
C
CH2
H2
H2C C
C CH2
H2
H2C
H2C
H2
C
C
H2
CH2
CH2
Cyclopropane
cyclobutane
cyclopentane
cyclohexane
Substituted cycloalkanes
H2
C
H2C C C CH3
H H2
H2
C
H2C
HC CH3
H2C
CH
CH3
ethylcyclopropane
1,2-dimethylcyclopentane
Reactions of alkanes
Combustion
 Substitution reactions
C2H6 + Cl2  C2H5Cl + HCl

Unsaturated hydrocarbons

alkenes CnH2n
double bond
contain a
H2C
ethylene or ethene C2H4
propylene or propene C3H6

CH2
alkynes CnH2n-2
contain a triple bond
acetylene C2H2
propyne C3H4
Sample alkenes
CH 3
CH 3
2-methyl-2-butene
H
CH 3
H 3C
CH 2
CH 3
2-pentene
H
CH 3CH=CH 2
H
Geometrical isomers
CH3CH=CHCH3
2-butene
CH3
CH3
CH3
H
H
H
H
CH3
cis-2-butene
trans-2-butene
Addition reactions
CH2=CH2 + Cl2
CH3CH=CHCH3 + H2
CH2Cl-CH2Cl
CH3CH2CH2CH3
example of hydrogenation
H3C
H3C
C
C
C
C
CH3
CH3
+
+
2Cl2
Cl2
H3C
H3C
CCl
CCl
CCl2 CCl2
CH3
CH3
Aromatic hydrocarbons
Functional Groups I
Functional Groups II
Alcohols; R-OH




The hydroxyl or alcohol functional group -OH
The OH group is polar; hydrogen bonding
makes alcohols more soluble in water than in
hydrocarbons
CH3OH methyl alcohol, methanol, “wood
alcohol”. Impurity in moonshine; causes
blindness
CH3CH2OH ethyl alcohol, ethanol, “alcohol”
Prepared by fermentation of sugarcontaining plant material.
Reactions with alcohols
The OH group does NOT make alcohols
basic. In fact, phenol is weakly acidic.
 An important reaction is esterification the formation of esters when an alcohol
reacts with an acid. See notes on
carboxylic acids

Ethers R-O-R
The -O- bridge
 CH3CH2-O-CH2CH3 is diethyl ether, or
“ether”. Used in medicine but not as
much as at one time. Very explosive!
 Ethers are used industrially as solvents

Aldehydes and Ketones
the carboxyl group C=O
O
R
C
H
Aldehyde
H
C
R
Ketone
C
H
formaldehyde
O
R
O
O
H3C
C
H
acetaldehyde
O
O
H3C C C2H5
dimethyl ketone ethyl methyl ketone
acetone
H3C
C
CH3
Aldehydes
Some aldehydes have common names like
formaldehyde and acetyaldehyde.
 The other way to name them is with the al
ending.
CH3CH2CHO is propanal or propyl aldehyde

Carboxylic Acids R-COOH
O
R C OH
Carboxylic acid
O
H C OH
methanoic acid
formic acid
O
H3C C OH
ethanoic acid
acetic acid
O
CH3CH2 C OH
propionic acid
Alcohol Aldehyde  Carboxylic
acid
OH
OH
R
C
H
H
C
OH
H
H
methanol
H
alcohol
H3C
C
H
H
ethanol
oxidation - remove hydrogen
O
O
R
C
H
Aldehyde
H
C
O
H
formaldehyde
H3C
C
H
acetaldehyde
oxidation - add oxygen
R
C
O
O
O
OH
Carboxylic acid
H
C
OH
methanoic acid
formic acid
H3C
C
OH
ethanoic acid
acetic acid
Esters




Carboxylic acid + alcohol  ester + water
For organic chemists, reactions that
generate water are called condensation
reactions
The condensation reaction is called
esterification
Fruity smell. Pentyl acetate (amyl acetate)
gives bananas their smell but is very
poisonous in large amounts.
Esterification
H
O
R
C
OH
+
HO
C
H
O
R'
R
C
O
C
H
carboxylic acid
CH3CH2
C
H
ester
alcohol
OH
+
HO
C
H
O
H
O
CH3
CH3CH2
C
O
ethanol
C
H
H
propionic acid
R'
ester
et hy l propanat e
CH3
Hydrolysis of ester
Ester + water  carboxylic acid +
alcohol
 The reverse of esterification
 When done using a base (NaOH, for
example), the reaction is called
saponification.
 Soap was made by reacting fat (esters of
stearic acid and glycerin) with NaOH to
get sodium stearate.

Amines R-NH2 , R2NH, R3N





Organic chemistry’s base.
Think of amines as substituted ammonia
NH3 + R  RNH2  R2NH  R3N
Just as NH3 is an proton acceptor making NH4+
, so amines are proton acceptors.
They also react with carboxylic acids to give
amides
Horrid smell. One is called putricine, another
cadaverine
Amines
CH3NH2
methylamine
CH3CH2NH2
ethylamine
CH3
(CH3)NH
H3C
dimethylamine
N
H
Amides
carboxylic acid + amine  amide
H
O
R
C
OH
+
H
acetic acid
R
H
C
N
OH
+
H
N
R'
amide
H
O
C
R'
amine
carboxylic acid
H3C
N
O
CH3
methylamine
H3C
O
H
C
N
methylacetamide
e s t er
et hy l pr opanat e
CH3
Amino acids

A compound with the carboxylic acid
group and the amine group
H
H2N
C
H
O
C
Glycine
OH
Peptides &Proteins
The amine group of one acid reacts with
the carboxylic acid group of another to
make a peptide
 When more molecules add on, we get a
polypeptide
 Certain polypeptides are of biological
importance - proteins

Stereoisomers; chirality
Carbohydrates




Have the general formula Cn(H2O)n
The simple sugars glucose and fructose are the
basic building units of many carbohydrates.
These sugar molecules can make rings.
Disaccharides like table sugar (sucrose) consists
of two rings joined together.
When many rings join we get starch or cellulose.
The difference is in how the rings are joined. We
can digest starch but not cellulose