Download FUNCTIONAL GROUPS

FUNCTIONAL
GROUPS
FUNCTIONAL GROUPS
• A functional group is a cluster of atoms within a molecule that have
specific reactivity patterns
• Compounds with the same functional group have similar physical
properties
• The general formula for an organic compound with a functional group is R
+ functional group
• R stands for the alkyl group (carbon chain)
• If there is more than one alkyl group, we use R’, R’’
PHYSICAL PROPERTIES AND FORCES
BETWEEN MOLECULES
• Physical properties are largely dictated by intermolecular forces
• There are three main types
• Hydrogen bonding strong intermolecular attraction between
• The H atom on a N-H, O-H, F-H group of one molecule and the N,
O, or F of another molecule
• Dipole-Dipole interactions: between polar molar molecules
• Dispersion forces: between all covalent molecules
• Very weak for small molecules, but they strengthen as the size of
the molecule get larger
SOME INTERESTING POINTS ABOUT
INTERMOLECULAR FORCES
SINGLE-BONDED
FUNCTIONAL GROUPS
1. ALCOHOLS
ALCOHOLS
PROPERTIES OF ALCOHOLS
2. ORGANIC HALIDES
PROPERTIES OF ORGANIC HALIDES
3. ETHERS
4. AMINES
PROPERTIES OF AMINES
PROPERTIES OF ETHERS
FUNCTIONAL GROPS WITH
THE C=O BOND
THE CARBONYL GROUP
• Found in many compounds
• One of the most interesting
functional groups
O
• The double bond makes it
more reactive the a C-O single
bond (in alcohols, ethers)
• Different reactivity patterns
CH2
1. ALDEHYDES AND KETONES
• Hydrocarbons with a C=O functional group
• If the carbonyl group is at the end of the parent chain, it is an
O
aldehyde
C
R
H
• If the carbonyl group is in the middle of the parent chain, it is an
ketone
R
O
O
C
C
H
R
R
Terminal carbonyl group gives an
aldehyde
Internal carbonyl group gives a
ketone
General formula: R-CHO
General formula: R-CO-R’
Examples
O
H3C
CH2
C
CH2
CH2
H
O
H3C
CH2
C
CH2
CH2
CH2
CH2
CH3
• Pentanal
• 3-octanone
• Aldehydes end in “–al”
• Ketones end in “–one”
PROPERTIES OF ALDEHYDES AND
KETONES
• The C=O is polar, so aldehydes and ketones are usually polar
• Hydrogen bonding cannot occur between molecules of these
compounds
• But, since oxygen has two lone pairs, it can form weak
hydrogen bonds with water
• The low molecule mass chains are soluble in polar solvents, as the
number of carbons increase, the solubility decreases
• Boiling points are lower than analogous alochols
• i.e. Ethanol = 78.9°C; Ethanal = 20.2°C
• Propanol = 97°C; Propanone (acetone) = 56°C
• Odours:
• Aldehydes: strong pungent
• Ketones tend to smell sweet
• They are good organic solvents for both polar and non-polar
compounds
• Acetone = propanone: one of the most common organic
solvents in chemistry labs
• Remember: like-dissolves-like
• These are polar/non-polar at the same time, so they can
dissolve both
2. CARBOXYLIC ACIDS
• The carboxyl group characterizes organic acids (proton donors)
• Recall: amines = organic bases
• These are always terminal, since they take up three of carbons four
bonds
• General formula: R-COOH
• Names always end in –oic acid
• Example: pentanoic acid
O
C
R
OH
PROPERTIES OF CARBOXYLIC ACIDS
• Similar to alcohols
• Hydrogen bonding occurs between chains and with water
molecules
• Melting and boiling points are higher than parent alkanes; increase
with number of carboxyl groups
• Have unpleasant odours
• The H on the OH means that it can easily donate the H to another
molecule
3. ESTERS
• Derivatives of carboxylic acids, where the ‘H’ of COOH has been
replaced with an alkyl group
O
• Combination of carboxylic acid and alcohols
• Names in “-oate”
R
C
R
O
1
PROPERTIES OF ESTERS
• Usually polar molecules
• Do not have O-H bond, therefore do not form hydrogen bonds with each
other
• Due to lone pairs on O atoms, can accept a hydrogen bon from water
• Low molecular masses are soluble in water and polar solvents
• Low boiling points, usually volatile liquids (combustible/explosive)
• Have pleasant odours and tastes
• Used as perfumes and artificial flavours
4. AMIDES
• Amides are derivatives of carboxylic acids, where the OH of the COOH
has replaced with an amine group
O
• Combining a carboxylic acid and an amine
• Can be primary amides, secondary or tertiary
• Names end in: “amide”
C
R
R
N
R
2
1
PROPERTIES OF AMIDES
• C-N, N-H, C=O bonds are polar, so molecules are usually polar
• Primary and secondary amides experience hydrogen bonding
• Soluble in water and other polar solvents, solubility decreases as the
number of carbons increases
• Primary amides have higher melting and boiling points than analogous
carboxylic acids
• Solid at room temperature
• Form the backbone of all proteins
Homework
• Practice Worksheet