Chapter 22: Hydrocarbon Compounds

Asymmetric carbon

A carbon with four different atoms or groups attached. Sometimes referred to as left-handed and right-handed.

Substitution reaction

A common type of organic reaction in which an atom, or group of atoms, replaces another atom or group of atoms. Substitution reactions are an important method of introducing new functional groups to organic molecules. For example, a halogen atom can replace a hydrogen atom on an alkane to produce a halocarbon.

Cyclic hydrocarbon

A compound that contains a hydrocarbon ring. Rings with five and six carbons are the most abundant. Cyclic hydrocarbons can also be saturated or unsaturated.

Cracking

A controlled process by which hydrocarbons are broken down or rearranged into smaller, more useful molecules. For example, fractions containing compounds of higher molar mass are cracked to produce the more useful short-chain components of gasoline and kerosene. Hydrocarbons are cracked with the aid of a catalyst and with heat. This process also produces low-molar-mass alkanes that are used to manufacture paints and plastics.

Homologous series

A group of carbons form a homologous series if there is a constant increment of change in molecular structure from one compound in the series to the next. A CH2 group is the increment of change in straight-chain alkanes.

Alkyl halide

A halocarbon in which a halogen is attached to a carbon of an aliphatic chain.

Aryl halide

A halocarbon in which a halogen is attached to a carbon of an arene ring

Alkane

A hydrocarbon in which there are only single covalent bonds. In any alkane, all the carbon-carbon bonds are single covalent bonds and all the other bonds are carbon-hydrogen bonds. The carbon atoms in an alkane can be arranged in a straight chain or a chain that has branches.

Alkyl group

A hydrocarbon substituent that is derived from an alkane. Simply, an alkane with one of the hydrogens removed. Can be one carbon or several carbons long. Named by removing -ane from the parent hydrocarbon name and adding -yl. The three smallest alkyl groups are the methyl group (-CH3), the ethyl group (C2CH3), and the propyl group (-CH2CH2CH3).

Alkene

A hydrocarbon that contains one or more carbon-carbon double covalent bonds. At least one carbon-carbon bond in an alkene is a double covalent bond. Other bonds may be single carbon-carbon bonds and carbon-hydrogen bonds. Ethene (C2H4) is the simplest alkene.

Alkyne

A hydrocarbon that contains one or more carbon-carbon triple covalent bonds. At least one carbon-carbon bond in an alkyne is a triple covalent bond. Other bonds may be single or double caron-carbon bonds and carbon-hydrogen bonds. Alkynes, like alkenes, are unsaturated compounds. the simplest alkyne is ethyne (C2H2).

Functional Group

A specific arrangement of atoms in an organic compound that is capable of characteristic chemical reactions. Most organic chemistry involves the functional groups of organic molecules. The double and triple bonds of alkenes and alkynes are chemically reactive, therefore double and triple carbon-carbon bonds functional groups. Organic compounds can be classified according to their functional groups.

Cycloalkane

AA cyclic hydrocarbon that contains only single bonds and is therefore saturated.

Straight-chain alkane, 3 examples

An alkane that contains any number of carbon atoms, one after the other, in a chain. Examples: ethane, propane, butane

Branched-chain alkane

An alkane with one or more alkyl groups formed when a substituent alkyl group is attached to a straight chain hydrocarbon.

Substituent

An atom or group of atoms that can take the place of a hydrogen atom on a parent hydrocarbon molecule. All carbon atoms or groups of carbon atoms that are not part of the parent alkane.

Aromatic compound

An organic compound that contains a benzene ring or other ring in which the bonding is like that of benzene.Benzene is the simplest aromatic compound. When two or more equally valid structures can be drawn for a molecule, resonance occurs. The actual bonding of the benzene ring does not alternate between the two extreme resonance structures. Rather, all bonds in the ring are identical hybrids of single and double bonds. In a benzene molecule, the bonding electrons between carbon atoms are shared evenly around the ring. Benzene and other molecules that exhibit resonance are more stable than similar molecules that do not exhibit resonance.

Halocarbon

An organic compound that contains at least one covalently bonded fluorine, chlorine, bromine, or iodine atom. The general formula of a halocarbon is RX, where X is a halogen substitutent. The IUPAC rules for naming halocarbons are based on the name of the parent hydrocarbon. The halogen groups are named as substitutents. Common names of halocarbons consist of two parts: the first part names the hydrocarbon portion of the molecule as an alkyl group, such asmethyl- or ethyl-. The second part names the halogen with an -ide ending. Attractions between halocarbon molecules are primarily the result of weak van der Waals interactions. Generally, these attractions increase with the degree of halogen substitution meaning that more highly halogenated organic compounds have higher boiling points.

Unsaturated compound

An organic compound that contains double or triple carbon-carbon bonds. The ratio of hydrogen atoms to carbon atoms is lower in an unsaturated compound than in a saturated compound.

Hydrocarbon

An organic compound that contains one carbon and one hydrogen. These are the simplest organic compounds. The simplest hydrocarbons are methane (CH4) and ethane (C2H6).

Saturated compound

An organic compound that contains the maximum number of hydrogen atoms per carbon atom. Alkanes are saturated compounds because the only bonds in alkanes are single covalent bonds.

Aliphatic compound

Any compound not classified as an aromatic compound. (Alkanes, Alkenes, Alkynes, and Cycloalkanes).

Carbon bonds

Because carbon had four valence electrons, a carbon atom always forms four covalent bonds. The ability of carbon to form stable carbon-carbon bonds is one reason that carbon can form so many different compounds.

Melting and boiling points of straight-chain alkanes

Both melting and boiling points of straight-chain alkanes increase as the number of carbons increases.

Substituted Aromatic Compounds

Compounds containing substituents attached to a benzene ring. Named using benzene as the parent hydrocarbon. When the benzene ring is a substituent, the C6H5 group is called a phenyl group.

Isomers

Compounds that have the same molecular formula but different molecular structures. Examples: Butane and 2-methylpropane (C4H10).

Constitutional isomers

Compounds that have the same molecular formula, but the atoms are joined together differently. Constitutional isomers differ in physical properties such as boiling point and melting point. They also have different chemical reactivities. In general, the more highly branches the hydroarbon structure is, the lower the boiling point of he isomer will be compared with less branched isomers.

Natural gas, components, and combustion

Contains mostly aliphatic hydrocarbons. Natural gas is an important source of alkanes of low molar mass. Made up of about 80% methane, 10% ethane, 4% propane, and 2% butane. The remaining 4% consists of nitrogen, helium, and hydrocarbons of higher molar mass. Propane and butane are separated from the other gases in natural gas by liquefaction. Complete combustion of a hydrocarbon produces a blue flame. Incomplete combustion of a hydrocarbon produces a yellow flame. The yellow color is due to the formation of small, glowing carbon particles that are deposited as soot when they cool. Carbon monoxide also forms along with carbon dioxide and water during incomplete combustion.

Disubstituted benzenes

Derivatives of benzene that have two substituents. In the IUPAC naming system, the possible positions of two substituents in disubstituted benzene are designated 1,2; 1,3; or 1,4. Common names for distributed benzenes use the terms ortho, meta, and para (abbreviated as o,m, and p) in place of numbers.

Naming an alkene

Find the longest chain in the molecule that contains the double bond. This chain is the parent alkene. It has the root name of the alekene with the same number of carbons plus the ending -ene. The chain is numbered so that the carbon atoms of the double bond have the lowest possible numbers. Substituents on the chain are named and numbered in thee same way they are for alkanes.

Naming a cycloalkane

First count the number of carbons in the ring and assign the corresponding alkane name. Then simply add the prefix cyclo- to the alkane name.

Benzene structure

First described by Friedrich Kekule. The benzene molecule is a six membered carbon ring with one hydrogen atoms attached to each carbon. This arrangement leaves one electron from each carbon free to participate in a double bond. Two different structures with alternating double bonds can be written for benzene.

Coal, formation, composition, distillation, and products

Geologists believe that some 300 million years ago when the huge tree ferns and mosses that grew abundantly in swampy tropical regions dies, they formed thick layers of decaying vegetation which has been covered by layers of soil and rock, building up an intense pressure. This pressure, together with heat from the earth's interior, slowly turned the plant remains into coal. The first stage in the formation of coal is an intermediate, soft, brown, spongy, fibrous material known as peat. After a long period of time, peat loses most of its fibrous texture and becomes lignite, or brown coal. Coal is classified by its hardness and carbon content. Lignite then forms bituminous coal after continuous pressure and heat change. In some areas, such high pressure turns soft coal into anthracite, or hard coal. Coal consists largely of cond ensed aromatic compounds of extremely high molar mass. These compounds have a high proportion of carbon compared with hydrogen. Coal also contains a small amount of sulfur. As coal burns, the sulfur oxidizes to form SO2 and SO3, two major air pollutants that contribute to acid rain and smog. Coke is the solid material left after coal distillation. It is used as a fuel in many industrial processes and is the crucial reducing agent in the smelting of iron ore.

Cis-trans isomers

Have atoms joined in the same order, but the spatial orientation of the groups differs. Although cis-trans isomerism is possiblein other molecules, the most common example occurs in molecules with double bonds.

International Union of Pure and Applied Chemistry (IUPAC) and the first 10 hydrocarbons

IUPAC established rules for naming straight-chain alkanes. Methane (CH4), Ethane (C2H6), Propane (C3H8), Butane (C4H10), Pentane (C5H12), Hexane (C6H14), Heptane (C7H16), Octane (C8H18), Nonane (C9H20), Decane (C10H22)

Stereoisomers

Molecules in which the atoms are joined in the same order, but the positions of the atoms in space are different. Two types of stereoisomers are cis-trans isomers and enantiomers.

Enantiomers

Pairs of molecules that are mirror images and not superimposable. Unlike other isomers, enantiomers have identical physical properties such as boiling points and densities. They do, however, behave differently when they interact with other molecules that have asymmetric carbons. As a result, each enantiomer can have a different effect on the body.

Friedrich Wohler

Refuted the idea that a mysterious vital force directed the formation of carbon compounds by using inorganic substances to synthesize urea in 1828.

Cis configuration

Similar groups are on the same side of the double bond.

Trans configuration

Similar groups extend from opposite sides of the double bond.

Condensed structural formula

Some bonds and/or atoms are left out of the structural formula

Properties of Hydrocarbons

The electron pair in a carbon-hydrogen bond or a carbon-carbon bond is shared almost equally by the nuclei of the atoms forming the bond, therefore making hydrocarbons nonpolar molecules. The attractions between nonpolar molecules are weak van der Waals forces. So hydrocarbons with low molar masses tend to be gases or liquids that boil at a low temperature.

Parent alkane

The longest continuous carbon chain of a branched-chain hydrocarbon.

Boiling points for alkenes and alkynes

The major attractions between alkenes and alkynes are weak van der Waals forces, therefore, the introduction of a double or triple bond into a hydrocarbon does not have a dramatic effect on physical poperties such as boiling point.

Naming branched-chain alkanes

The name of a branched-chain alkane is based on the name of the longest continuous carbon chain. Each substituent is naamed according to the length of its chain and numbered according to its position on the main chain.

Primary, Secondary, Tertiary, and Quaternary carbons

The number of carbons attached to the carbon in question.

Petroleum, components, refining

The organic compounds found in petroleum are more complex than those in natural gas. Most of the hydrocarbons in petroleum are straight-chain alkanes, but petroleum also contains small amount of aromatic compounds and sulfur-, oxygen-, and nitrogen- containing compounds. Crude oil is a mix of hydrocarbons having anywhere from one carbon to more than 40 carbon atoms. Petroleum refining begins with the distillation of crude oil into fractions according to boiling point.

Organic chemistry

The study of almost all carbon compounds regardless of their origin.