Transcript Functional Groups III

Slide 1
Functional Groups III
Functional Groups III
Slide 2
Halogenoalkanes

Organic compounds with one or more halogens in place of
hydrogen are called halogenoalkanes or alkyl halides.

These compounds are named as alkanes with the halogen as a
substituent.

The group names for the halogens are fluoro-, chloro-, bromo-,
and iodo-.
Example:
1 - iodopropane
I
H
H
H
C
C
C
H
H
H
H
Slide 3
Halogenoalkanes
Name the following alkyl halides:
CH3CH2CH2CH2Br
C
C
C
C
C
Br
C
C
C
C
C
Slide 4
Physical Properties of
Halogenoalkanes

Halogenoalkanes have relatively low boiling points.

The only methyl halide which is a liquid at room temperture is
iodomethane; chloroethane is a gas

The boiling points reflect the intermolecular forces of
halogenalkanes; van der Waals forces.

As the carbon chain increases in size the boiling point rises due
to increased intermolecular forces.

There is also an increase in boiling point as you go from a
chloride to a bromide to a iodide (for a given number of carbon
atoms) is also because of the increase in number of electrons
leading to larger van der Waals forces.

There are a lot more electrons in iodomethane than there are in
chloromethane.
Slide 5
Physical Properties of
Halogenoalkanes
Slide 6
Physical Properties of
Halogenoalkanes

The carbon-halogen bonds are polar, because the electron pair
is pulled closer to the halogen atom then the carbon.

This is because the halogens are more electronegative then
carbon.

This means that in addition to the dispersion forces (van der
waals) there will be forces due to the attraction between the
permanent dipoles.

The size of the dipole-dipole attractions will fall as the bonds
get less polar (as you go from chloride to bromide to iodide, for
example(.

Nevertheless, the boiling points rise! This shows that the effect
of the permanent dipole-dipole attractions is much less
important than that of the temporary dipoles which causes the
dispersion forces.
Slide 7
Physical Properties of
Halogenoalkanes

The location of the halogen on the carbon chain also effect the
boiling point.

The temporary dipoles are greatest for the longest molecules.

The attractions are also stronger if the molecules can lie closely
together.
C
C
C
C
Br
C
375 K
C
C
Br
364 K
C
C
C
Br
346 K
C
C
Slide 8
Physical Properties of
Halogenoalkane

Halogenoalkanes are only slightly soluble in water.

It is difficult for the dispersion and dipole-dipole forces to
overcome the hydrogen bonding of water molecules.

Halogenoalkanes tend to dissolve in organic solvents which
have similar intermolecular forces.
Slide 9
Amines



Amines can be considered
derivates of ammonia in which
one ore more hydrogen have
been replaced by alkyl groups.
Primary amines have one alkyl
group bonded to the nitrogen,
secondary amines have two
groups on the nitrogen, tertiary
amines have three groups and
quaternary ammonium salts
have four.
There are several different ways
to name amines that are
accepted by IUPAC.
H3C
CH2
CH2
H3C
CH2
CH2
NH
H3C
CH2
CH2
N
CH3
NH2
CH3
CH3
Slide 10
Amines

Most amines are prefixed by the word amino -, with the location
of the NH2 – group being indicated: for example, 2 –
aminopentane and 1,6 – diaminohexane.

It is also correct to call them by the longest alkane with the
suffix – amine: for example, pentan-2-amine.

However, when the number of carbon atoms is small (one, two
or three), the old names of methylamine, ethylamine and
propylamine tend to be used rather than aminomethane,
aminoethane and aminopropane.

IUPAC accepts 1 – butylamine, 1 – butanamine and 1 –
aminobutance for CH3CH2CH2CH2NH2
Slide 11
H3C CH2
CH2
CH2
NH2
1 – butylamine, 1 – butanamine and 1 – aminobutance
H3C
CH2
CH2
NH2
Slide 12
Amines

In the case of secondary amines the main name of the amine is
taken from the longest carbon chain attached to the nitrogen
atom.

The other chain is prefixed as an alkyl group, with the location
prefix given as an italic N.


Examples include N – methylethanamine and N –
ethylpropanamine.
For tertiary amines there are two prefixes with an italic N: for
example, CH3CH2N(CH3)2 is N, N – dimethyethanamine.
Slide 13
CH3
H3C
CH2
N
CH3
N,N - dimethylethanamine
H3C
CH2
CH2
NH
CH3
Slide 14
Physical Properties of Amines

Amines have relatively high boiling points because they can
form hydrogen bonds with each other as well as van der Waals
dispersion forces and dipole-dipole interactions.

The longer the carbon chain the greater the van der Waals
dispersion forces and therefore the higher boiling point.

Primary amines have higher boiling points than secondary
amines due to the nitrogen being in the middle of the secondary
amine; causes a lower dipole-dipole attraction.

Tertiary amines have much lower boiling points due to the lack
of hydrogen atoms on the nitrogen and therefore absence of
hydrogen bonding with themselves.
Slide 15
Physical Properties of Amines

Smaller amines are very soluble in water; they are able to form
hydrogen bonds with water (even tertiary amines).

The solubility decreases as the carbon chain increases as
would be expected.
Slide 16
Amides

Amides are derived from carboxylic acids.

A carboxylic acid contains the – COOH group, and in a amide
the – OH part of that part is replaced by an – NH2 group.

So amides contain the – CONH2 group.

The name of amides are derived from the acid by replacing “oic acid” ending with “amide”.
Methanamide: HCONH2
Ethanamide: CH3CONH2
Propanamide: CH3CH2CONH2
Slide 17
Amides

If the chain was branched, the carbon in the –CONH2 group
counts as the number 1 carbon atom.
C
3
C
2
C
1
C
O
N
C
3 - methylbutanamide
Slide 18
Physical Properties of Amides

The boiling points of the amides are high for the size of the
molecules because they can form hydrogen bonds.

The hydrogen atoms in the –NH2 group are sufficiently positive
to form a hydrogen bond with a lone pair on the oxygen atom of
another molecule.

Small amides are also soluble in
water do to their ability to form
hydrogen bonds with water.
Slide 19
Nitriles
Nitries (R – CN) used to be called cyanides, so that C2H2CN
was known as ethyl cyanide.


The IUPAC way of naming nitriles is to consider the acid from
which they are derived, as the – COOH group has been
replaced by a – CN group.


The suffix – nitrile is added to the hydrocarbon forming the
basis of the acid.
For example, C2H5CN now becomes propanenitrile, and
ethanenitrile has the formula CH3CN
Slide 20
CH2
H3C
C
N
propanenitrile
H3C
C
ethanenitrile
N