Chemistry Chapter 14: Introduction to Organic Chemistry

CHEMISTRY KEYWORDS:

Single Covalent Bond: A bond made up of a pair of electrons shared between 2 atoms.

Sigma bond (σ bond): Single covalent bond formed by the ‘end-on’ overlap of atomic orbitals.

Pi (π) bond: Covalent bond formed by ‘sideways’ overlap of p and p or p and d atomic orbitals.

Structural Isomers: Compounds with the same molecular formula but different structural formulae.

Stereoisomers: Compounds whose molecules have the same atoms bonded to each other in the same way, but with a different arrangement of atoms in space so that the molecules cannot be superimposed on each other.

Geometrical Isomerism: Displayed by unsaturated or ring compounds with the same molecular formula and order of atoms but different shapes. It arises because of a lack of free rotation about a double bond (due to the pressure of π (pi) bond) or a ring structure.

Enantiomers: Pair of optically active molecules whose mirror images cannot be superimposed.

Chiral Centre: Carbon atom with 4 different atoms or groups of atoms attached. This allows optical isomers to exist.

Reaction Mechanism: A series of steps that take place in the course of the overall reaction.

Free-radical Reaction: a 3-step reaction that starts with the production of reactive atoms or molecules with an unpaired electron. The second step regenerates free radicals. Then the reaction finishes with 2 free radicals meeting to form a molecule.

Carbocation: Alkyl group with a single positive charge on one of its carbon atoms. It is formed in reaction mechanisms.

Electron Deficient: Atom or molecule that has less than its usual share of electrons.

Inductive Effect: Uneven sharing of electrons along a covalent bond. Electron-donating species, such as an alkyl group, are said to have a positive inductive effect, whereas electron-withdrawing species, such as oxygen atoms, have a negative inductive effect.

Electrophile: Species in organic chemistry that can act as an electron pair acceptor.

Nucleophile: Species that can act as a donor of a pair of electrons.

Addition Reaction: Organic reaction in which 2 or more molecules combine to give a single product molecule.

Elimination Reaction: A reaction in which a small molecule, such as H₂O or HCl, is removed from an organic molecule.

Condensation Reaction: A reaction in which 2 organic molecules join together and in the process eliminate a small molecule, such as water or hydrogen chloride.

Substitution Reaction: Reaction that involves the replacement of 1 atom, or group of atoms by another.

Oxidation Reaction: Addition of oxygen, removal of electrons or increase in oxidation number of a substance; in organic chemistry this refers to a reaction in which oxygen atoms are added to a molecule and/or hydrogen atoms are removed from a molecule.

Reduction Reaction: Removal of oxygen, the addition of electrons or decrease in oxidation number of a substance; in organic chemistry, it is the removal of oxygen atoms from a molecule and/or the addition of hydrogen atoms to a molecule.

Free-radical Substitution: Reaction in which halogen atoms substitute for hydrogen atoms in alkanes. The mechanism involves steps in which reactive free radicals are produced (initiation), regenerated (propagation) and consumed (termination).

 

CHEMISTRY DEFINITIONS:

Structural Formula: Formula that shows how many, and the symbols of, atoms bonded to each carbon atom in an organic molecule.

Displayed Formula: 2D representation of an organic molecule, showing all its atoms (by their symbols) and their bonds (by short single, double, or triple lines between the symbols).

Skeletal Formula: Simplified displayed formula with all C and H atoms and C-H bonds removed.

Homologous Series: Group of organic compounds having the same functional group, the same general formula and similar chemical properties.

Functional Group: Atom or group of atoms in an organic molecule which determines the characteristic chemical reactions.

General Formula: A formula representing a homologous compound series using letters and numbers.

Aliphatic Compounds: Straight-chain or branched-chain organic compounds and cyclic organic compounds that do not contain benzene rings.

 

CHEMISTRY IMPORTANT NOTES:

No. of C atoms	Molecular Formula	Name of alkane	Prefix
1	CH4	Methane	Meth-
2	C2H6	Ethane	Eth-
3	C3H8	Propane	Prop-
4	C4H10	Butane	But-
5	C5H12	Pentane	Pent-
6	C6H14	Hexane	Hex-
7	C7H16	Heptane	Hept-
8	C8H18	Octane	Oct-
9	C9H20	Nonane	Non-
10	C10H22	Decane	Dec-

 

Homologous Series	General Formula	Example	Structural Formula
Alkenes	CnH2n	Ethene	CH2 = CH2
Halogenalkanes	CnH2n+1X X = F, Cl, Br, I	Chloromethane	CH3Cl
Alcohols	CnH2n+1OH	Methanol	CH3OH
Aldehydes	CnH2n+1CHO	Ethanal	CH3CHO
Ketones	CnH2n+1COCmH2m+1	Propanone	CH3COCH3
Carboxylic Acids	CnH2n+1COOH	Ethanoic Acid	CH3COOH
Esters	CnH2n+1COOCmH2m+1	Propyl Ethanoate	CH3COOC3H7 CH3COOCH2CH2CH3
Amines	CnH2n+1NH2	Methylamine	CH3NH2
Nitriles	CnH2n+1CN	Ethanenitrile	CH3CN

 

Homologous Series	Example	Structural Formula
Alkenes	But-2-ene	CH3CH=CHCH3
Halogenalkanes	2-chloropropane	CH3CHClCH3
Alcohols	Butan-1-ol	CH3CH2CH2CH2O
Aldehydes	Butanal	CH3CH2CH2CHO
Ketones	Butanone	CH3COCH2CH3
Carboxylic Acids	Butanoic Acid	CH3CH2CH2COOH
Esters	Ethyl Propanoate	CH3CH2COOCH2CH3
Amines	Butylamine	CH3CH2CH2CH2NH2
Nitriles	Butanenitrile	CH3CH2CH2CN

 

SUMMARY:

We can represent an organic molecule, with increasing detail, by using its:

·       Empirical Formula

·       Molecular Formula

·       Structural Formula

·       Displayed Formula

·       3D Displayed Formula

Functional groups give organic compounds their characteristic reactions.

Important functional groups include alkenes, alcohols, halogenoalkanes, aldehydes, ketones, carboxylic acids, esters, amines and nitriles.

The shapes of organic molecules can be explained by the sigma and pi bonds between carbon atoms, and the hybridisation of their atomic orbitals.

There are 2 types of isomers: Structural Isomers and Stereoisomers.

Structural isomers have the same molecular formula but different structural formulae. We can group these into position, functional group or chain isomers.

Stereoisomers have the same molecular formula but different arrangement of their atoms in space.

·       Cis/trans isomers arise because of the restricted rotation around a C=C double bond.

·       Optical isomers contain a chiral centre (carbon atom bonded to 4 different atoms of group of atoms), resulting in mirror images of the molecule that cannot be superimposed.