3.3.1 Introduction to organic chemistry

Empirical formula

A formula that gives the simplest whole number ratio of atoms of each element in a compound

Molecular formula

A formula that gives the actual number of atoms of each element in a molecule

General formula

An algebraic formula that can describe any member of a family of compounds

Structural formula 

A structural formula shows the atoms carbon by carbon, with the attached hydrogens and functional groups

Displayed formula

A way of representing a molecule that shows how all the atoms are arranged and all the bonds between them

Skeletal formula

A simplified organic formula which only shows the carbon skeleton and associated functional groups

Nomenclature

A fancy word for naming things in a particular organic compound

Naming straight-chain alkanes

Naming branched alkanes

Count the number of carbons in the longest chain

Identify the type of side chains and where they are placed on the longest chain

Side chains are written in alphabetical order

Naming branched alkanes (two or more of the same side groups)

If there are two or more side chains of the same type then you add a prefix of di- for two, tri- for three

(You should ignore these prefixes when you’re putting the other prefixes in alphabetical order)

Naming cycloalkanes

Cycloalkanes have the same name as their straight-chain alkane equivalent, but with cyclo- attached to the front

If there’s more than one alkyl group (ethyl, methyl), then make the numbers as low as possible, and the alkyl that’s first alphabetically goes on the 1-carbon

Naming other functional groups (alkenes)

Priority of functional groups

If there is more than one functional group, the one with the highest priority is the main functional group, hence the stem of the name comes from it

Mechanisms

Mechanisms break reactions down into a sequence of stages

Reaction mechanism diagrams

Show how molecules react together by using curly arrows to show which bonds are made or broken

The formation of a covalent bond is shown by a curly arrow that starts from the lone electron pair or from another covalent bond

The breaking of a covalent bond is shown by a curly arrow starting from the bond

Structural isomers

A molecule with the same molecular formula, but a different structural formula to another molecule

(e.g. the atoms are connected in different ways)

Chain isomers

An organic molecule that contains the same atoms and functional groups as another molecule but has a different arrangement of the carbon skeleton

(e.g. either straight chains or branched chains)

Position isomers

A molecule with the same skeleton and molecular formula as another molecule but with the functional group attached to a different carbon

Functional group isomers

A molecule with the same molecular formula as another molecule, but with the atoms arranged into different functional groups

Stereoisomers

A molecule that has the same structural formula as another molecule but with the atoms arranged differently in space