Understanding Points
Structure 3.2.1—Organic compounds can be represented by different types of formulas. These
include empirical, molecular, structural (full and condensed), stereochemical and skeletal.
Structure 3.2.2—Functional groups give characteristic physical and chemical properties to a
compound. Organic compounds are divided into classes according to the functional groups present in their molecules.
Structure 3.2.3—A homologous series is a family of compounds in which successive members differ by a common structural unit, typically CH2. Each homologous series can be described by a general formula.
Structure 3.2.4—Successive members of a homologous series show a trend in physical properties.
Structure 3.2.5—“IUPAC nomenclature” refers to a set of rules used by the International Union of
Pure and Applied Chemistry to apply systematic names to organic and inorganic compounds.
Structure 3.2.6—Structural isomers are molecules that have the same molecular formula but
different connectivities.
Empirical, Molecular, Structural Formulas
•
Molecular formula - ratio of actual number of atoms in a compound
•
Empirical formula - simplest whole number ratio of atoms in a compound
Homologous Series
1.
Same general formula (+ functional group)
2.
Similar chemical properties
3.
Successive members differ by CH2 group
4.
A gradual increase in physical properties
Stem | Homologous Series (General Formula) | |||||||
Alkane
CnH2n+2 | Alkene
CnH2n | Alkyne
CnHn | Halogenoalkane
CnH2n+1X | Alcohol
CnH2n+1OH | Carboxylic Acid
Cn-1H2n-1COOH | Aldehyde
CnH2nO | Ketone
CnH2nO | |
Meth | -ane | N/A | N/A | halogeno-...-ane | -anol | -anoic acid | -anal | N/A |
Eth | -ene | -yne | ||||||
Prop | -anone | |||||||
But | ||||||||
Pent | ||||||||
Hex |
Boiling point
Hydrocarbon skeleton | Carbon no. ↑
london dispersion forces ↑
b.p. ↑
Methane ~ butane: gas
Pentane ~ hexane: liquid |
Branching ↑
contact b/w molecules ↓
intermolecular forces ↓
b.p. ↓ | |
Functional group | carboxylic acid (highest b.p) > alcohol > ketone > aldehyde > halogenoalkane > alkane (lowest b.p.)
Hydrogen bonding > dipole-dipole interaction > london dispersion forces |
Solubility
Water | H bonding functional group (most soluble) > polar functional group > non-polar function group (least soluble) |
Branching ↑
Contact between H bonding functional group and water ↓
Solubility ↓ | |
Non-polar solvent (e.g. hexane) | non-polar function group (most soluble) > polar functional group > H bonding functional group (least soluble) |
Branching ↑
Contact between non-polar hydrocarbon skeleton and non-polar solvent ↑
Solubility ↑ |
Primary, Secondary and Tertiary Compounds
1) Alcohols and Haloegenoalkanes
•
number of carbon atoms attached to central C atom (bonded to a functional group)
2) Amines
•
Amines are named according to the number of carbon atoms attached to the N atom
◦
Primary amine : 1 carbon atom and 2 hydrogen atoms
◦
Secondary amine: 2 carbon atoms and 1 hydrogen atom
◦
Tertiary amine: 3 carbon atoms
Nomenclature - IUPAC system
1.
Identify the longest straight carbon chain and the number of carbons in it
2.
Identify the functional group and its position
3.
Identify the side chains or substituent groups
1. No. of carbon atoms in hydrocarbon skeleton, e.g. meth-, eth-, prop-... hex-
Number of carbon atoms | Stem in IUPAC name | Example | Name of the molecule |
1 | Meth- | CH4 | Methane |
2 | Eth- | C2H6 | Ethane |
3 | Prop- | C3H8 | Propane |
4 | But- | C4H10 | Butane |
5 | Pent- | C5H12 | Pentane |
6 | Hex- | C6H14 | Hexane |
2. Identify the main functional group and its position
Class | Example | Functional Group | Suffix |
Alkane
CnH2n+2 | Ethane | N/A | -ane |
Alkene
CnH2n | Ethene | Alkenyl
-C=C- | -ene |
Alkyne
CnHn | Ethyne | Alkynyl
-C≡C- | -yne |
Alcohol
CnH2n+1OH | Ethanol | Hydroxyl
-OH | -anol |
Aldehyde
R-CHO | Ethanal | Carbonyl
-CHO | -anal |
Ketone
R-CO-R’ | Propanone | Carbonyl
-C=O- | -anone |
Carboxylic Acid
Cn-1H2n-1COOH | Ethanoic acid | Carboxyl
-COOH | -anoic acid |
Ester
R-COO-R’ | Ethyl ethanoate | Ester
-COO- | -yl...-anoate
(R’-yl R-anoate) |
Ether
R-O-R’ | methoxyethane | Ether
-O- | -oxy…-ane
(R-oxy R’-ane if R’ > R) |
Amine
R-NH2 | ethanamine | Amine
-NH2 | -anamine |
Amide
R-CONH2 | propanamide | Carboxyamide
-CONH2 | -anamide |
Nitrile
R-C≡N | propanenitrile | Nitrile
-C≡N | -anenitrile |
Arene
C6H5-R | methyl benzene | Phenyl
C6H5- | -yl benzene |
•
Difference b/w aldehyde and ketone
1. Carbonyl position at the end vs middle of carbon skeleton
2. Presence vs absence of hydrogen bonded to carbonyl
•
Position Number, e.g. Propan-2-ol, but-1-ene
3. Identify the side chains or substituent groups
Class | Example | Functional Group | Prefix |
Side Hydrocarbon Chain
(Alkyl Chain) | 2-methyl propane
CH3CH(CH3)CH3 | Hydrocarbon chain which is not the longest | -yl
Methyl, Ethyl, Propyl |
Halogenoalkane
CnH2n+1X | Bromomethane
CH2BrCH3 | -F, -Cl
-Br, -I | halogeno…-ane |
Amine
R-NH2 | 3-amino propanoic acid
CH2(NH2)CH2COOH | Amine
-NH2 | amino- |
•
amine acts as functional group on its own but substituent if another functional group present
Two substituents
2 substituents | Identical | Non-identical |
Same position | 2,2-dibromobutane | 2-bromo-2-chlorobutane
*alphabetical ordering |
Different position | 1,2-dibromobutane | 2-chloro-1-iodobutane
*alphabetical ordering |
Two (identical) functional groups (in different positions)
Structural Isomers
•
Same molecular formula but different structural formula
•
e.g. C5H12