Download An Introduction to Functional Groups in Organic Chemistry What are

What are Functional Groups
An Introduction to Functional
Groups in Organic Chemistry
„
„
Functional groups are common bonding
patterns found in organic molecules
Examples
O
O
C
H
C
CH3
HO
Reactivity of Functional Groups
CH3
a carboxylic acid
an aldehyde
Reactivity of Functional Groups
O
O
2 Li + 2 H2O → 2 LiOH + H2
+ Tollen's Reagent
C
H
+ silver mirror
C
HO
CH3
CH3
2 Na + 2 H2O → 2 NaOH + H2
O
2 K + 2 H2O → 2 KOH + H2
O
+ Tollen's Reagent
C
H
CH2CH3
+ silver mirror
C
HO
CH2CH3
1
Functional Groups Containing
Carbon and Hydrogen Only
Reactivity of Functional Groups
O
O
+ Tollen's Reagent
C
H
„
atoms, and therefore possess only single
bonds.
+ silver mirror
C
HO
R
R
O
HO
„
no silver mirror
produced
+ Tollen's Reagent
C
R
Alkanes contain only sp3 hybridized carbon
A compound is only called an alkane if it contains
none of the other functional groups.
„
Alkenes contain at least one carbon-carbon
„
Alkynes contain at least one carbon-carbon
double bond.
O
O
CH2
C
C
H
OH
+ Tollen's Reagent
???
triple bond.
Cyclic Hydrocarbons
„
CH2CH3
CH3
C CH3
CH3
an alkane
CH3
H
H
C C
CH3
an alkene
H C C CH3
„
„
an alkyne
„
An alkane which contains a ring made up of three
or more atoms is called a cycloalkane.
Likewise, a cycloalkene contains a carbon-carbon
double bond somewhere in a ring of carbon atoms.
Cycloalkynes are relatively rare, for reasons we will
see later (think bond angles).
We will not consider these as distinct functional
groups
„
We still classify a cycloalkene as an alkene
a cycloalkane
a cycloalkene
2
Aromatics
„
„
Alkyl Halides
The term aromatic has a rather detailed meaning which we
will discuss next semester.
For now, when we describe a compound as containing an
aromatic group, we mean to say that it contains a benzene
ring.
„
„
Three equivalent ways of representing the benzene molecule
„
„
Note that the benzene ring is not considered either an alkene
or a cycloalkene; the special term aromatic makes the
presence of the ring and double bonds understood.
As we shall see, aromatic compounds react in distinctly
different ways than do alkenes, owing to delocalization of
electrons within the ring.
Alcohols
„
H
H
Technically, the carbon should be sp
hybridized.
OH
H
C
C
CH3
„
alcohols.
H3C
a halogen atom bonded to a carbon
atom somewhere in the molecule.
We are sometimes more specific, calling
a compound an alkyl chloride, alkyl
bromide, etc.
H
Cl
H
C
Br
CH3
Thiols and Amines
Compounds which contain the hydroxyl
group -OH bonded to carbon (R–OH)
make up the class of compounds called
„
Alkyl halides are compounds which have
CH3
3
„
Thiols are similar to alcohols in
structure, with a sulfur atom replacing
the oxygen atom: R–SH
Amines have a nitrogen atom bonded to
at least one carbon atom; the
remainder of its bonds may be to
carbon or hydrogen.
OH
3
Thiols and Amines
H3C
C
Ethers
OH
H
CH3
alcohols
„
thiols
„
OH
SH
H
H3C
C
CH3
The ether functional group is described as
an sp3 oxygen atom bonded to two carbon
atoms, and may be symbolized as R-O-R'.
R and R' may be the same groups or
different.
SH
CH3
CH3
H
amines
N
H3C
C
CH3CH2
CH3
CH3
O
CH3
CH2CH3
O
Carbonyl-Containing Functional
Groups
„
C
CH3
NH2
A carbonyl group is made up of a carbon atom
double bonded to an oxygen atom. The carbon
atom is not bonded to any other heteroatom.
O
CH3
O
Ketones
„
„
The ketone functional group contains a carbonyl
group, with the carbon of that group bonded to
two other carbon atoms.
R and R' may or may not be the same.
C
O
C
the carbonyl group
„
We will not consider the carbonyl group to be a
functional group in-and-of itself; rather, it is the
essential portion of two functional groups:
aldehydes and ketones.
R
R'
a ketone
4
Aldehydes
„
„
Carboxylic Acids
The aldehyde functional group contains a
carbonyl group, with the carbon of that group
bonded to at least one hydrogen atom. The
other bond is either to a carbon atom or another
hydrogen atom.
R is an alkyl group or another hydrogen atom in
the case of formaldehyde.
„
C
C
OH
O
carboxylic acid
the carboxyl group
„
„
C
O
O
O
R
A carboxyl group looks similar to a carbonyl group, but at
least one of its sigma bonds is to a second oxygen atom.
H
The carboxylic acid functional group has a hydrogen atom
bonded to this oxygen atom. It is generally acidic, for
reasons we discussed in Chapter One.
The other bond need not be specified; it may be an alkyl
group, a hydrogen atom, or another –OH.
an aldehyde
Carboxylic Acid Derivatives
„
„
There are several functional groups which are
structurally similar to carboxylic acids.
The ester functional group has an alkyl group in
place of the hydrogen bonded to the carboxylic
oxygen atom.
O
Carboxylic Acid Derivatives
„
C
R
C
O
R'
an anhydride
OR'
an ester
„
O
O
C
R
The anhydride functional group is a two-sided
carboxyl group:
„
R and R' may or may not be the same.
R and R' may or may not be the same.
5
Carboxylic Acid Derivatives
„
The acid chloride (or acyl chloride) functional
group has a chlorine atom in place of the
carboxylic oxygen
Carboxylic Acid Derivatives
„
An amide has an sp3 hybridized nitrogen atom in
place of the carboxylic oxygen atom.
O
O
C
R
N
C
R
Cl
an amide
an acid chloride
„
„
„
Practice
The nitrogen atom is bonded to 0-2 alkyl groups.
The remaining bonds are to hydrogen.
Do not confuse amides with amines!
Practice—Solutions
Circle and label all the functional groups in the molecules below.
OH
CH2
CH3
CH
O
C
Cl
CH3
alcohol
O
C
CH3
ether
CH2
CH
ester
O
O
OH
O
C
Cl
CH3
CH3
O
C
F
alkyne
C
N
SH
CH3
CH
O
H3C
CH3
ether
O
C
CH3
O
SH
alkyl halide
aldehyde
O
alkyl halide
O
H
O
ketone
CH3
H
alkene
CH
N
thiol
H3C
CH3
amine
F
6