An Introduction to Functional Groups in Organic Chemistry What are ...

An Introduction to Functional
Groups in Organic Chemistry
What are Functional Groups
• Functional groups are common bonding
patterns found in organic molecules
• Examples
O
C
H CH 3
an aldehyde
O
C
HO CH 3
a carboxylic acid
Reactivity of Functional Groups
Reactivity of Functional Groups
O
O
2 Li + 2 H 2 O → 2 LiOH + H 2
H
C
+ Tollen's Reagent + silver mirror
C
CH 3
HO CH 3
2 Na + 2 H 2 O → 2 NaOH + H 2
O
O
2 K + 2 H 2 O → 2 KOH + H 2
H
C
CH 2CH 3
+ Tollen's Reagent
HO
C
CH 2CH 3
+ silver mirror
1

Reactivity of Functional Groups
Functional Groups Containing
Carbon and Hydrogen Only
H
HO
O
O
C
O
C
C
H
R
+ Tollen's Reagent C
R
+ Tollen's Reagent
CH 2
C
OH
O
HO
O
R
no silver mirror
produced
+ Tollen's Reagent
+ silver mirror
• Alkanes contain only sp 3 hybridized carbon
atoms, and therefore possess only single
bonds.
• A compound is only called an alkane if it contains
none of the other functional groups.
• Alkenes contain at least one carbon-carbon
double bond.
• Alkynes contain at least one carbon-carbon
triple bond.
Cyclic Hydrocarbons
CH 2 CH 3
CH 3 C CH 3
CH 3
an alkane
CH 3 H
C C
H CH 3
an alkene
H C C CH 3
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.
• Alkyl halides are compounds which have
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
H
H
C Cl H C
CH 3
CH 3
Br
Alcohols
• Compounds which contain the hydroxyl
group -OH bonded to carbon (R–OH)
make up the class of compounds called
alcohols.
• Technically, the carbon should be sp 3
hybridized.
H 3 C
H
C
CH 3
OH
Thiols and Amines
• 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
CH 3
H
H 3C C
OH
CH 3
H
H 3C C CH 3
SH
H
H 3C C
NH 2
OH
alcohols
SH
thiols
CH 3
N
amines
CH 3
Ethers
• The ether functional group is described as
an sp 3 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.
CH 3 CH 2 O CH 2 CH CH O
3 3
CH 3
C
CH 3
CH 3
O
Carbonyl-Containing Functional
Groups
• 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
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.
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.
R
O
C
R'
a ketone
4

Aldehydes
• 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.
R
O
C
H
an aldehyde
Carboxylic Acids
• A carboxyl group looks similar to a carbonyl group, but at
least one of its sigma bonds is to a second oxygen atom.
O
C
O
the carboxyl group
• 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.
O
C
OH
carboxylic acid
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
R
C
an ester
OR'
Carboxylic Acid Derivatives
• The anhydride functional group is a two-sided
carboxyl group:
R
• R and R' may or may not be the same.
O
C
O
O
C
an anhydride
R'
• 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
R
O
C
Cl
an acid chloride
Carboxylic Acid Derivatives
• An amide has an sp 3 hybridized nitrogen atom in
place of the carboxylic oxygen atom.
• The nitrogen atom is bonded to 0-2 alkyl groups.
• The remaining bonds are to hydrogen.
• Do not confuse amides with amines!
R
O
C
N
an amide
Practice
Circle and label all the functional groups in the molecules below.
OH
CH 3
O
CH 2 CH O C C
Practice—Solutions
ether
OH
CH 3
alcohol
O
CH 2 CH O C C
ketone
O
O
CH 3
Cl
CH 3
CH 3
O
H
ester
O
O
CH 3
Cl
CH CH 3
3
alkyl halide
alkene
alkyne
O
aldehyde
H
C
CH
C
CH
O
F
SH
H 3C
N
CH 3
ether
O
F
alkyl halide
SH
thiol
H 3C
N
CH 3
amine
6