FUNCTIONAL GROUPS. A functional group is a cluster of atoms within a molecule that have specific...
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![Page 1: FUNCTIONAL GROUPS. A functional group is a cluster of atoms within a molecule that have specific reactivity patterns Compounds with the same functional.](https://reader035.fdocuments.us/reader035/viewer/2022062408/56649f315503460f94c4c205/html5/thumbnails/1.jpg)
FUNCTIONAL GROUPS
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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’’
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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
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SOME INTERESTING POINTS ABOUT INTERMOLECULAR FORCES
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SINGLE-BONDED FUNCTIONAL GROUPS
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1. ALCOHOLS
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ALCOHOLS
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PROPERTIES OF ALCOHOLS
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2. ORGANIC HALIDES
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PROPERTIES OF ORGANIC HALIDES
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3. ETHERS
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4. AMINES
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PROPERTIES OF AMINES
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PROPERTIES OF ETHERS
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FUNCTIONAL GROPS WITH THE C=O BOND
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THE CARBONYL GROUP
• Found in many compounds
• One of the most interesting functional groups
• The double bond makes it more reactive the a C-O single bond (in alcohols, ethers)
• Different reactivity patternsCH2
O
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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 aldehyde
• If the carbonyl group is in the middle of the parent chain, it is an ketone
C
O
HR
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C
O
HR
Terminal carbonyl group gives an aldehyde
General formula: R-CHO
C
O
RR
Internal carbonyl group gives a ketone
General formula: R-CO-R’
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Examples
• Pentanal
• Aldehydes end in “–al”
C
O
HCH2
CH2CH2
CH3 C
O
CH2CH2
CH2CH2
CH3 CH2CH3
• 3-octanone
• Ketones end in “–one”
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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
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• 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
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• 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
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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 C
O
OHR
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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
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3. ESTERS
• Derivatives of carboxylic acids, where the ‘H’ of COOH has been replaced with an alkyl group
• Combination of carboxylic acid and alcohols
• Names in “-oate”
C
O
ORR
1
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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
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4. AMIDES
• Amides are derivatives of carboxylic acids, where the OH of the COOH has replaced with an amine group
• Combining a carboxylic acid and an amine
• Can be primary amides, secondary or tertiary
• Names end in: “amide”
C
O
NRR
1
R2
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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
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Homework
• Practice Worksheet