Ch 15Hydrocarbons — Class 11 Chemistry, concept-first.

A hydrocarbon is any compound built from just two elements, carbon and hydrogen. Hydrocarbons are organised along two independent lines: whether the carbon skeleton is an open (acyclic) chain or a clo…

Alkanes are aliphatic saturated hydrocarbons: every bond in the molecule is a carbon-carbon or carbon-hydrogen single covalent bond, with no multiple bonds anywhere in the structure.

Alkanes containing more than three carbon atoms generally show structural isomerism, and specifically chain isomerism, in which the same molecular formula can be assembled either as one continuous (st…

Alkanes contain only single covalent (sigma) bonds, and a sigma bond -- formed by coaxial (head-on, cylindrically symmetric) overlap of orbitals along the bond axis -- keeps the same extent of orbital…

Alkanes are obtained industrially from crude petroleum and natural gas: dead plant matter buried for hundreds of millions of years under high temperature and pressure converted into crude oil, which c…

Carbon and hydrogen have almost identical electronegativity, so the C-H and C-C bonds throughout an alkane are essentially non-polar covalent bonds, making alkane molecules as a whole non-polar.

Alkanes are relatively unreactive toward acids, bases, and most common oxidising or reducing agents, but they do undergo four characteristic reactions under specified, fairly forcing conditions.

Alkanes find a range of practical uses that follow directly from their physical state and chain length.

Alkenes are unsaturated hydrocarbons that contain at least one carbon-carbon double bond. An alkene with exactly one C=C double bond has two hydrogen atoms fewer than the alkane with the same number o…

Alkenes with more than three carbon atoms show both structural isomerism and geometrical isomerism. Structural isomerism in alkenes includes both chain isomerism (the carbon skeleton itself differs) a…

The most industrially important alkenes -- ethene, propene, and buta-1,3-diene -- along with all alkenes up to four carbons, can be obtained in pure form from petroleum products; ethene specifically i…

Alkenes are non-polar or, at most, weakly polar compounds. They are insoluble in water but soluble in non-polar organic solvents such as benzene, ether and chloroform, and they are less dense than wat…

Alkenes are considerably more reactive than alkanes because the pi electrons of the C=C double bond are held less tightly than the electrons of a sigma bond and are exposed above and below the plane o…

Alkenes serve chiefly as starting materials for a wide range of other functional-group compounds: alkyl halides, alcohols, aldehydes, ketones, and carboxylic acids are all commonly built up from an al…

Alkynes are aliphatic unsaturated hydrocarbons containing at least one carbon-carbon triple bond (C-triple-bond-C).

Alkynes show position isomerism, which is a form of structural isomerism: the same molecular formula can place its carbon-carbon triple bond at different points along an identical carbon chain.

Ethyne is manufactured industrially by two distinct routes. The first is controlled, high-temperature (1773 K) partial oxidation of methane: six molecules of methane react with two of dioxygen to give…

The physical properties of alkynes closely resemble those of alkanes and alkenes already described in sections 15.1.4 and 15.2.3: alkynes are less dense than water, insoluble in water, and reasonably…

Alkynes undergo the same broad family of addition reactions already met for alkenes (hydrogenation, halogenation, hydrohalogenation, hydration), typically adding TWICE over since a triple bond has two…

Ethyne (acetylene) has several important industrial and everyday uses. It is a key starting material for manufacturing ethanal (acetaldehyde), propanone (acetone) and ethanoic acid (acetic acid) -- ea…

Aromatic hydrocarbons, also called arenes, are hydrocarbons whose structure and chemical behaviour resemble benzene, the simplest and most fundamental aromatic compound.

Benzene, molecular formula C6H6, is the parent compound from which most other aromatic compounds are conceptually derived.

Benzene's molecular formula, C6H6, carries a high degree of unsaturation on paper, and both open-chain and cyclic structures with double and/or triple bonds could in principle be drawn for it.

Benzene's characteristic preference for substitution reactions over addition reactions is not unique to benzene alone -- it is a general property, called aromaticity or aromatic character, shared by a…

Coal tar and petroleum are the major industrial sources of aromatic compounds generally, exactly as they are for benzene specifically (section 15.4.1).

Benzene is a colourless liquid at room temperature, boiling at 353 K and melting at 278.5 K. It is essentially insoluble in water and, being less dense than water, forms a separate upper layer when th…

Aromatic compounds are chemically characterised above all by electrophilic substitution reactions, in which a ring hydrogen is replaced by an electrophile while the aromatic ring itself, with its reso…

Because all six hydrogens on unsubstituted benzene are chemically equivalent, a single electrophilic substitution on benzene itself can only ever give one product.

Benzene is both toxic (section 15.4.5) and, separately, carcinogenic (cancer-causing) -- a hazard serious enough that benzene is sometimes described as 'the mother of all carcinogens', since a large n…