Ch 12Hydrocarbons — Class 11 Chemistry, concept-first.

A hydrocarbon is an organic compound whose molecule is built from carbon and hydrogen atoms only -- no oxygen, nitrogen, halogen or any other element.

IUPAC nomenclature of alkanes. The name of an alkane is built in three steps: (1) identify the longest continuous carbon chain -- this fixes the parent name (methane, ethane, propane, butane, pentane,…

Although the carbon-carbon bond in ethane, , is drawn as a single line, the two groups are free to rotate about that sigma bond, because a sigma bond is cylindrically symmetric about its axis and rota…

Alkanes are non-polar (or only very weakly polar) molecules: carbon and hydrogen have similar electronegativities, so individual and bonds carry negligible dipole character, and the molecule as a whol…

Despite being described as relatively unreactive, alkanes do undergo one characteristic reaction with the halogens (chlorine and bromine most readily; fluorine reacts explosively and iodine barely rea…

Combustion. Alkanes burn readily in an excess (plentiful supply) of oxygen to give carbon dioxide, water and a large amount of heat -- the reaction that makes them valuable as fuels (LPG, petrol, dies…

Alkenes are named by the same longest-chain rule as alkanes, except that the parent chain must include both carbons of the double bond, the ending changes from '-ane' to '-ene', and the chain is numbe…

Because rotation about a carbon-carbon double bond is restricted (breaking it would mean breaking the pi bond), the two substituents attached to each doubly-bonded carbon are frozen in a fixed spatial…

Like the alkanes, alkenes are essentially non-polar molecules with only weak dispersion forces between them, so their physical-property trends run parallel to the alkanes': boiling points rise with ch…

The pi bond of an alkene is an exposed, comparatively loosely held region of electron density above and below the plane of the molecule, which makes it attractive to electrophiles -- electron-deficien…

Ozonolysis. Passing ozone gas into a solution of an alkene forms an unstable cyclic intermediate called an ozonide, which is not usually isolated but is immediately decomposed by a reductive work-up -…

Alkynes are named on the same longest-chain, lowest-locant principle as alkanes and alkenes, but with the suffix '-yne': the parent chain must include both triple-bonded carbons, numbered from whichev…

Preparation. The simplest and industrially most important alkyne, ethyne (acetylene), is manufactured by treating calcium carbide with water: Calcium carbide is itself made by heating calcium oxide (q…

Benzene, , is a perfectly flat, hexagonal molecule in which all six carbon atoms are equivalent -- a fact that early structural theories struggled to explain simply by drawing three alternating single…

Benzene's delocalised pi electron cloud makes the ring, like an alkene's pi bond, attractive to electrophiles -- but because addition across any one carbon-carbon bond would destroy the resonance-stab…

The Friedel-Crafts reactions are two closely related electrophilic aromatic substitutions, discovered by Charles Friedel and James Crafts, that attach a carbon-based substituent -- an alkyl group (alk…

Benzene and the larger fused-ring aromatic compounds called polycyclic aromatic hydrocarbons (PAHs) -- naphthalene, benzo[a]pyrene and their relatives, which are produced whenever an organic fuel (woo…

This chapter surveyed the four families of hydrocarbons -- compounds of carbon and hydrogen only -- moving from the least to the most reactive.

Sample papers and previous-year board questions for this subject.