Organic chemistry: Definitions AS

Alicyclic

An aliphatic compound arranged in non-aromatic rings (with or without side chains)

Aliphatic

Compound containing carbon and hydrogen atoms joined in straight or branched chains or in non-aromatic rings

Alkane

Homologous series with the general formula CnH2n+2

Alkyl

Group with the general formula CnH2n+1

Aromatic

A compound containing a benzene ring

Curly arrow

Shows the movement of a pair of electrons

Curly arrows must start from a bond, a lone pair of electrons or a negative charge

Dipole

A partial charge on an atom which is caused by the differing electronegativities of atoms in a covalent bond

Displayed formula

The relative positions of atoms and the bonds between them

Empirical formula

Simplest whole number ratio of atoms of each element present in a compound

Functional group

Group of atoms responsible for the characteristic reactions of a compound

General formula

Simplest algebraic formula of a member of a homologous series (e.g: alkane = CnH2n+2)

Heterolytic fission

When a covalent bond breaks, one bonding atom receives both electrons from the bonded pair

Homologous series

Series of organic compounds containing the same functional group with successive members differing by -CH2

Homolytic fission

When a covalent bond breaks, each bonding atom receives one electron from the bonding pair forming two radicals

IUPAC

International Union of Pure and Applied Chemistry

Molecular formula

Number and type of atoms of each element in a molecule

Nomenclature

Naming system for compounds

Organic compound

Carbon-containing compounds

Radical

Species with an unpaired electron (e.g: Cl*)

Reaction mechanism

Series of steps that represent the overall reaction by showing the breaking and forming of bonds using curly arrows

Saturated

Organic compound containing only C—C single bonds

Skeletal formula

Simplified organic formula shown by removing hydrogen atoms from alkyl chains leaving the carbon skeleton and functional groups

Structural formula

Minimal detail that shows the arrangement of atoms in a molecule (e.g: butane = CH3(CH2)2CH3)

Structural isomers

Compounds with the same molecular formula but different structural formulae

Unsaturated

Organic compound which contains at lease one C=C double bond, a C=-C triple bond or an aromatic ring

Sigma bond (o-)

Type of covalent bond which forms when atomic orbitals overlap head on

Sigma (o-) bonds can rotate freely

Boiling point

Temperature at which a liquid boils and becomes gas

Shorter, more branched alkanes have higher boiling points as there are weaker London forces between the molecules which require less energy to overcome

Bond enthalpy

The energy required to break one mole of gaseous bonds

Actual bond enthalpies may differ from the average as the average bond enthalpy considers a particular bond in a range of molecules

Complete combustion

When a compound is burnt in a plentiful supply of oxygen

When alkanes are completely combusted the only products are water and carbon dioxide

Covalent bond

Strong bond formed between two atoms due to the electrostatic attraction between a shared pair of electrons and the atomic nuclei

Electron pair repulsion

Pairs of electrons around a nucleus repel each other so the shape that a molecule adopts has these pairs of electrons positioned as far apart as possible

Carbon atoms in alkanes have a tetrahedral shape and a bond angle of 109.5’

Homolytic fission

When a covalent bond breaks, each bonding atom receives one electron from the bonding pair forming two radicals

Hydrocarbon

Compound containing only hydrogen and carbon

Incomplete combustion

When a compound is burnt in a limited supply of oxygen

When alkanes are incompletely combusted, water, carbon monoxide, particulates and some carbon dioxide may be produced

Initiation

The first step in a radical substitution mechanism involving the formation of radicals

(E.g: Br—Br → Br* + *Br)

London forces

Induced dipole-dipole interactions caused when the random movement of electrons creates a temporary dipole in one molecule which then induces a dipole in the neighbouring molecule

Polar bond

Covalent bond that has a permanent dipole due to the different electronegativities of the atoms that make up the bond

Propagation

Intermediate steps in a radical substitution mechanism where a radical reacts with another species

(E.g: CH4 + Br* → *CH3 + HBr

: *CH3 + Br2 → CH3Br + Br*)

Radical

Species with an unpaired electron

Radical substitution

Type of substitution in which a radical replaces another atom/group of atoms in a compound

Alkanes can undergo radical substitution with chlorine or bromine in the presence of UV light forming a mixture of organic products (further substitution or reactions at different positions may occur)

Saturated

Organic compound containing only C—C single bonds

Termination

Final steps in a radical substitution mechanism in which 2 radicals react together to form a species which only contains paired electrons

(E.g: Br* + *Br → Br2

: *CH3 + *CH3 → C2H6

: *CH3 + *Br → CH3Br)

Tetrahedral

Shape of a molecule in which the central atom has 4 bonding pairs of electrons

Sigma (o-) bond

Type of covalent bond which forms when atomic orbitals overlap head on

Sigma bonds can rotate freely

Pi bond

Type of covalent bond formed when adjacent p-orbitals overlap overlap sideways both above and beyond the bonding C atoms

Pi bonds can’t be rotated

Pi bonds have low bond enthalpy and so alkenes are more reactive than alkanes

Addition polymerisation

Formation of a long chain molecule when many monomers join together (polymer is the only product)

Addition reaction

Reaction in which molecules combine to form a single product

Alkene

Organic compound containing at least one C=C double bond

Biodegradable

Substance that can be decomposed by bacteria or other living organisms

Bond enthalpy

Energy required to break one mole of gaseous bonds

Actual bond enthalpies may differ from average bond enthalpies as the average bond enthalpy considers a particular bond in a range of molecules

Cahn-Ingold-Prelog (CIP) priority rules

Set of rules used to identify whether a stereoisomer is E or Z

Atoms with a higher atomic number have higher priority

If the highest priority substituents are on the same side of the double bond it’s the z-isomer

If the highest priority groups are on opposite sides it’s the E-isomer

Cis-Trans isomerism

Type of E/Z isomerism where the two substituent groups attached to the carbon atoms are the same

Cis isomers have the highest priority substituents on the same side of the double bond

Trans isomers have the highest priority substituents on opposite sides of the double bond

Covalent bond

Strong bond formed between 2 atoms due to the electrostatic attraction between a shared pair of electrons and the atomic nuclei

Electron pair repulsion (alkenes)

Pairs of electrons around a nucleus repel each other so the shape that a molecule adopts has these pairs of electrons positioned as far apart as possible

Carbon atoms in alkenes have a trigonal planar shape and bond angles of 120’

Electrophile

Electron pair acceptor

Electrophilic addition

Reaction in which the pi bond is broken and two new sigma bonds form as a result of the addition of an electrophile

E/Z isomerism

Type of stereoisomerism caused by the restricted rotation of pi bonds

Two different groups must be attached to each carbon atom of the C=C group

Z isomers have the highest priority substituents on the same side of the double bond

E isomers have the highest priority substituents on opposite sides of the double bonds

Heterolytic fission

When a covalent bond breaks one bonding atom receives both electrons from the bonding pair resulting in oppositely charged atoms

Markownikoff’s rule

Used to predict what the major product of an addition reaction will be when H—X is added to an unsymmetrical alkene

H attaches to the less substituted carbon to generate the more stable carbocation intermediate

Monomer

Small molecule used to form polymers

Photodegradable

Substance that can be broken down by light

Polymer

Large molecules made from many small units bonded together

Primary carbocation

Molecule in which the carbon with the positive charge is only attached to one alkyl group

Least stable carbocation

Repeat unit

Structure within a polymer that appears over and over again

Joining many repeat units forms a polymer

Secondary carbocation

Molecule in which the carbon with the positive charge is attached to two alkyl groups

More stable than a primary carbocation but less stable than a tertiary carbocation

Stereoisomers

Compounds with the same structural formula but a different arrangement of atoms in space

Tertiary carbocation

Molecule in which the carbon with the positive charge is attached to three alkyl groups

Most stable carbocation

Test for unsaturated compounds

Containing a C=C double bond, triple bond or aromatic ring means bromine water will be decolourised

Alcohol

Organic compound containing the OH functional group

Polarity of the OH functional group means alcohols can form hydrogen bonds and are soluble in water (when the chains are short)

Alcohols have a relatively low volatility compared with alkanes

Aldehyde

Organic compound containing -CHO functional group

Aldehydes can be formed from the oxidation of primary alcohols using Cr2O7^2-/H^+ and distillation

Alkene

Compound containing a C=C double bond

Can be formed from alcohols via the elimination of H2O using an acid catalyst and heat

Carboxylic acid

Organic compound containing -COOH functional group

Can be formed from the oxidation of primary alcohols using Cr2O7^2-/H^+ and reflux

Combustion

Rapid exothermic reaction of a substance with oxygen

Elimination

Type of reaction in which 2 atoms/group of atoms are removed from a molecule

Haloalkanes

Organic compound containing a halogen atom bound to an alkyl chain

Haloalkanes can be formed from alcohols via a substitution reaction with halide ions in the presence of acid

Ketone

Organic compound containing the C=O functional group in the middle of an alkyl chain

Can be formed by the oxidation of a secondary alcohol

Oxidation in relation to alcohols

Loss of electrons/increase in oxidation number

Alcohols can be oxidised using Cr2O7^2-/H^+

Oxidising agent

Substance that can oxidise another species while being reduced

Polar bond

Covalent bond in which there is an unequal share of electrons between the two atoms due to the differing electronegativities of the atoms involved

One atom has a partial positive charge and the other has a partial negative charge

Primary alcohol

Alcohol in which the OH is attached to a primary carbon atom

Can be oxidised to form either an aldehyde or a carboxylic acid depending on conditions

Secondary alcohol

Alcohol in which the OH is attached to a secondary carbon atom

Can be oxidised under reflux with Cr2O7^2-/H^+ to form a ketone

Tertiary alcohol

Alcohol in which the OH is attached to a tertiary carbon atom

Cannot be oxidised

Bond enthalpy (haloalkanes)

Energy required to break one mole of gaseous bonds

Bond enthalpy of the carbon-halogen bond in haloalkanes decreases from C—F to C—I

CFC

Class of compound made up of carbon, fluorine and chlorine used as refrigerants and aerosol propellants

CFC’s can be broken down by UV light in the upper atmosphere to form chlorine radicals which catalyse the breakdown of ozone

Haloalkane

Organic compound containing a halogen atom bound to an alkyl chain

Hydrolysis

Breakdown of a compound as a result of a reaction with water

Rate of haloalkane hydrolysis for different carbon-halogen bonds can be determined via a reaction with water in the presence of AgNO3 and ethanol

Nucleophile

Electron pair donor

Nucleophilic substitution

Reaction in which an electron pair donor attacks an electrophilic atom (atom with a partial or full positive charge) to replace an atom/group of atoms

Ozone

Molecule with the formula O3 which absorbs UV light in the atmosphere

Breakdown of ozone can be catalysed by chlorine radicals as well as other radicals such as *NO

Radical

Species with an unpaired electron

Substitution

Reaction in which one atom/group of atoms replaces another

Haloalkanes can undergo substitution reactions with aqueous alkali or with water

Rate of reaction increase from C—F to C—I due to the increasing bond enthalpy of the carbon-halogen bond

Anhydrous salt

Salt such as MgSO4 or CaCl2 which is used to remove traces of water from an organic solution

Distillation

Technique in which a liquid is heated, then the vapour is cooled and collected in a separate flask to the reaction mixture

During distillation the condenser must be positioned horizontally

Quickfit apparatus

Glassware that easily fits together in a variety of arrangements

Redistillation

Technique used to purify an organic liquid using multiple distillations

Reflux

The continuous boiling and condensing of a reaction mixture

Ensures the reaction goes to completion

During reflex the condenser must be positioned vertically

Separating funnel

Piece of apparatus that is used to purify an organic liquid by removing the organic layer from an aqueous layer

Synthetic route

Series of steps that are followed to make a specific compound

Elemental analysis

Sample is analysed to determine the proportion of elements that make up the compound present

Done by converting a known amount of an unknown sample into simple known compounds

Fragmentation

During mass spectrometry, unstable molecular ions break down into smaller fragments