Examples of functional groups, homologous series, general formula, displayed formula, graphic formula, molecular formula, skeletal formula, structural formula, empirical formula of molecules etc. are all explained with links to more examples of structure and naming and quizzes and reaction equations, reaction conditions and mechanisms.

Revision notes for GCE Advanced Subsidiary Level AS Advanced Level A2 IB Revise AQA GCE Chemistry OCR GCE Chemistry Edexcel GCE Chemistry Salters Chemistry CIE Chemistry revising courses for pre-university students (equal to US grade 11 and grade 12 and Honours/honors level courses)

A functional group is an atom or combination of atoms which gives an organic molecule its distinctive and characteristic chemistry. The term 'functional' group is linked to the concept of a homologous series. A homologous series is a group of molecules with the same general formula and the same functional group. They have similar physical and chemical properties (albeit with trends e.g. increasing boiling point with increasing carbon chain length). The terms higher/lower refer to a larger/smaller or longer/shorter carbon chain.

Note on structure 'styles' of representation

An empirical formula is the simplest whole number ratio of the atoms in a compound as found by experiment i.e. chemical analysis. It gives no structural information and may or may not be the same as the molecular formula e.g. CH₄ is both the empirical formula and the molecular formula of methane. However, the molecular formula of the butane molecule is C₄H₁₀ but its empirical formula is C₂H₅. The molecular formula of a glucose sugar molecule is C₆H₁₂O₆ but its empirical formula is only CH₂O !

A molecular formula e.g. C₃H₆O₂, gives a summary of all the atoms in the molecule, but gives no information on structure.

A structural formula - minimal/abbreviated/shortened e.g. orgives a 'limited' structure of a molecule but unambiguous in terms of interpreting ALL atom-atom links and no/some individual bonds may be shown.

A structural formula - full/displayed/graphical e.g. where all the individual atoms and bonds are shown. However it can be acceptable to show some side-chain groups in an abbreviated form e.g. methylpropane

where the side-chain methyl group may be written in the abbreviated form, but take car in exams!

A structural formula with full 3D spatial representation e.g. which shows the shape of the molecule and implies bond angles (in this case all are 109^o).

A skeletal formula e.g. in which no H atoms bonded to carbon atoms are shown, the lines represent either carbon-carbon bonds (single, double or triple), but other lines are needed to show bonds to other atoms which are NOT carbon or hydrogen e.g. C-Cl in and hydrogen atoms are shown if they are bonded to non-carbon atoms e.g. the -OH in.

A general formula sums up the formulae a series of compounds e.g. a homologous series of chemically similar compounds with closely related formulae e.g. the only difference may be more/less -CH₂- groupings in the carbon longest chain. There are many examples quoted throughout the rest of this page in the style C_xH_yO_z etc. where x, y and z are variables like 1, 2, 3 etc. but they related for a particular homologous series e.g. for saturated non cyclo alkanes the general formula is

C_nH_2n+2 for alkanes, so that n=1 generates the formula for methane CH₄ and n=5 generates the formula for pentane C₅H₁₂ etc. and .....

C_nH_2n+1COOH is the general formula for monocarboxylic acids, so that n=0 generates the formula for methanoic acid HCOOH and n=4 generates the formula for pentanoic acid CH₃CH₂CH₂CH₂COOH (so do not assume n always indicates the total carbon atoms in a molecule!).

However in all cases, the IUPAC systematic name is derived from the longest carbon chain, so both meth... (for one carbon) and pent... (for five carbons) occur in the names of the examples above.

Associated links other than those given for each homologous series below:

1. Notes on intermolecular forces between organic molecules and their effect on boiling point for various homolgous series, includes comparitive boiling point plots

2. Molecule shapes and bond angles

3. Covalent bonding - basic notes

FUNCTIONAL GROUPS and HOMOLOGOUS SERIES

nomenclature, structure and representation in pictures-graphics

ALKANES or cycloalkanes HYDROCARBONS (saturated)

…ANE, e.g. ALKANES, saturated hydrocarbons i.e. no double or triple bonds.

They can be linear, branched, cyclo, substituted etc. (see later - haloalkanes etc.) …

 butane,pentylcyclohexane,cyclopropane

2,2-dimethylpropane,2,2,3-trimethylbutane

Exemplar homologous series: C_nH_2n+2 for non-cyclo alkanes (n=1,2,3 etc.)

and C_nH_2n for cycloalkanes (n=3,4,5 etc.) isomeric with non-cyclo alkenes

further Notes and examples of the structure and nomenclature of alkanes

Multiple choice Quiz on naming alkanes * Type in an alkane name Quiz

Notes on selected reactions of alkanes from a mechanistic point of view but giving general equations and reaction conditions too

ALKENE HYDROCARBONS (unsaturated)

 …ENE, ALKENES, unsaturated hydrocarbons with a carbon=carbon C=C double bond functional group (ene)

They can have more than one C=C, be linear, branched, cyclo …

pent-1-ene,3-ethylpent-1-ene,cyclobuta-1,3-diene

orbuta-1,3-diene,  cyclohexene

further Notes and examples of the structure and nomenclature of alkenes

Multiple choice Quiz on naming alkenes * Type in an alkene name Quiz

Exemplar homologous series: C_nH_2n for non-cyclo alkenes (n=2,3 etc. with one C=C bond)  isomeric with cycloalkanes

and C_nH_2n-2 for cycloalkenes (n=3,4,5 etc., and with one C=C bond)

Notes on selected reactions of alkenes from a mechanistic point of view but giving general equations and reaction conditions too

ALKYNE HYDROCARBONS (unsaturated)

 …YNE e.g. ALKYNES, unsaturated hydrocarbons with a CC triple bond functional group (yne) e.g.

ethyne, and  propyne

Exemplar homologous series: C_nH_2n-2 for non-cyclo alkynes (with one triple bond)

 'ARENES' are aromatic hydrocarbons with at least one benzene ring functional group e.g. …

orbenzene,ormethylbenzene

further Notes and examples of the structure and nomenclature of aromatic compounds

further Notes and examples of aromatics  * Type in an alkane name Quiz

Notes on selected reactions of aromatic compounds (arenes) from a mechanistic point of view but giving general equations and reaction conditions too

Aliphatic: HALO… e.g. HALOGENOALKANES (HALOALKANES)

C-X halogen functional group where X = F fluoro…, Cl chloro.., Br bromo… or I iodo…

X is named as a prefix substituent in any type of organic molecule from alkanes to carboxylic acids.

chloromethane,bromoethane, dichlorodifluoromethane

1-bromo-1-chlorobutane,  iodocyclohexane

1,2-dibromocyclopentane,chloromethylbenzene

or phenylchloromethane, which can also be classified as an aromatic compound

BUT the halogen is not attached directly to the benzene ring so it is not an aryl halide)

Exemplar homologous series: C_nH_2n+1X for non-cyclo saturated halogenoalkanes (X=F,Cl,Br,I and n=1,2,3 etc.)

and C_nH_2n-1X for saturated cyclohalogenoalkanes (n=3,4,5 etc. with one C-X bond)

• A sub-CLASSIFICATION based on structural differences, which can have chemical consequences on e.g. rate of reaction or products formed in a reaction.

  • Halogenoalkanes are classified according to the atoms/groups attached to the carbon of the halogen atom X.

  • Primary halogenoalkanes have the structure R-CH₂-X, R = H, alkyl, aryl etc. i.e. apart from chloromethane they have one alkyl/aryl group attached to the C of the C-X group.

    • e.g. chloroethane CH₃CH₂Cl

  • Secondary halogenoalkanes have the structure R₂CH-X, R = alkyl or aryl etc. i.e. they have two alkyl/aryl groups attached to the C of the C-X group.

    • e.g. 2-bromobutane CH₃CHBrCH₂CH₃ 

  • Tertiary halogenoalkanes have the structure R₃C-X, R = alkyl or aryl etc. i.e. they have three alkyl/aryl groups attached to the C of the C-X group.

    • e.g. 2-iodo-2-methylpropane (CH₃)₃CI

further Notes and examples of the structure, classification and nomenclature of primary, secondary and tertiary haloalkanes - 3 pages

Multiple choice Quiz on naming haloalkanes * Type in a haloalkane name Quiz

Notes on selected reactions of halogenoalkanes (haloalkanes) from a mechanistic point of view but giving general equations and reaction conditions too

NOTE: Aromatic HALO ... ARENES (aromatic halogen compounds) have the halogen atom directly attached to the benzene ring.

chlorobenzene,1,4-dichlorobenzene,chloro-2-methylbenzene

ALCOHOLS (aliphatic, alkanols) and PHENOLS (aromatic)

Aliphatic …OH hydroxy functional group (ol) e.g. ALIPHATIC ALCOHOLS. Aliphatic alcohols are classified as primary, secondary and tertiary.

You can have diols, triols etc, with 2,3 etc, OH groups.

If there is a 'higher ranking' functional group in the molecule the substituent OH is called by the prefix 'hydroxy' see * examples.

Primary aliphatic alcohols R-OH where R is alkyl

ethanol,ethan-1,2-diol

or3-methylbutan-1-ol

4-hydroxybutanoic acid*

Secondary aliphatic alcohols R-CH(OH)-R' where R or R' are both alkyl (or aryl):

propan-2-ol,butan-2-ol,cyclohexanol,pentan-3-ol

cyclopentanol,  2-hydroxybutanoic acid*

Tertiary aliphatic alcohols RR'R"C-OH where R,R' or R" are all alkyl (or aryl):

or2-methylpropan-2-ol,2-methylbutan-2-ol

or 3-methylpentan-1-ol

Exemplar homologous series: C_nH_2n+1OH for saturated non-cyclic aliphatic alcohols (n=1,2,3 etc.)

or the less informative C_nH_2n+2O isomeric with aliphatic non-cyclo ethers

and C_nH_2n-1OH for cycloalcohols (n=3,4,5 etc. with one C-OH)

Notes and examples of the structure and nomenclature of aliphatic alcohols/alkanols

**further Notes and examples on types of alcohols and phenols

** linked to notes on oxidation of alcohols to aldehydes, ketones and carboxylic acids

 Multiple choice Quiz on naming alcohols * Type in an alcohol name Quiz

Notes on selected reactions of alcohols from a mechanistic point of view but giving general equations and reaction conditions too

AROMATIC PHENOLS ROH, R=aryl only,  when the -OH functional group is attached directly to a benzene ring the molecule is called a phenol.

If there is a 'higher ranking' functional group in the molecule the substituent OH is called by the prefix 'hydroxy' see * example.

ororphenol,2-chlorophenol,3-methylphenol

2,5-dichloro-4-methylphenol,3-hydroxybenzoic acid*

ETHERS

Alkyl/aryl…OXY…alkane/arene e.g. ETHERS which have the C-O-C linkage.

The smaller carbon chain with the oxygen atom, is given the prefix in the name alkyl/aryl..oxy…ane

(alkyl-O- groups like CH₃-O- are called alkoxy groups).

methoxymethane,methoxyethane,2-ethoxypropane

ethoxyethane,2-methoxypropane,

Exemplar homologous series: C_xH_2x+1-O-C_yH_2y+1 for saturated non-cyclo ethers (x or y =1,2,3 etc.)

or the less informative C_nH_2n+2O (n=2,3,4 etc.)  isomeric with non-cyclo aliphatic alcohols

or C_nH_2nO for cycloethers (n=2,3,4 etc. with one C-O-C linkage, non shown at the moment)

further Notes and examples of ethers and isomeric alcohols

ALDEHYDES and KETONES (a group of carbonyl compounds)

 …AL e.g. ALDEHYDES have the -CHO functional group at the end of a carbon chain e.g.

ethanal,propanal,or2-methylpropanal

butanal,pentanal,2-methylbutanal

Exemplar homologous series: C_nH_2n+1CHO for aliphatic aldehydes (n=0,1,2 etc.)

or the less in formative C_mH_2mO (m=1,2,3 etc.) isomeric with ketones and saturated cyclic aliphatic ethers

further Notes and examples of the structure and nomenclature of aldehydes

 multiple choice Quiz on naming aldehydes/ketones * type in name Quiz on naming aldehydes/ ketones

Notes on selected reactions of aldehydes/ketones from a mechanistic point of view but giving general equations and reaction conditions too

…ONE e.g. KETONES have the C-CO-C functional group linkage within the carbon chain:

propanone,orbutanone,pentan-2-one

  or     pentan-3-one

Exemplar homologous series: C_xH_xn+1-CO-C_yH_2y+1 for aliphatic ketones (x or y = 1,2,3, etc.)

or the less informative C_nH_2nO (n=3,4,5 etc.)  isomeric with aldehydes and saturated cyclic aliphatic ethers

 further Notes and examples of the structure and nomenclature of ketones

 multiple choice Quiz on naming aldehydes/ ketones * type in name Quiz on naming aldehydes/ ketones

Notes on selected reactions of aldehydes/ketones from a mechanistic point of view but giving general equations and reaction conditions too

CARBOXYLIC ACIDS

 …OIC ACID e.g. CARBOXYLIC ACIDS with the -COOH functional group, substituents quoted as prefixes (…dioic if 2 -COOH groups) e.g.

aliphatic carboxylic acids

methanoic acid,propanoic acid,*aminoethanoic acid

2-methylpropanoic acid, *2-hydroxybutanoic acid

pentanoic acid,  * ethanedioic acid

* examples of a dicarboxylic acids

If there is a 'higher ranking' functional group in the molecule the

substituent OH/NH₂ is called by the prefix 'hydroxy/amino see * examples.

Exemplar homologous series: C_nH_2n+1COOH for saturated aliphatic mono carboxylic acids (n=0,1,2,3 etc.)

or the less informative C_nH_2nO₂ (n=1,2,3,4 etc.) isomeric with aliphatic esters

aromatic carboxylic acids (-COOH directly attached to the ring)

* 3-hydroxybenzoic acid,2-ethanoylhydroxybenzoic acid (Aspirin!)

2-chlorobenzoic acid,   * benzene-1,2-dicarboxylic acid

(sometimes carboxylic rather than oic is used e.g. the dicarboxylic acids of benzene)

further Notes and examples of the structure and nomenclature of carboxylic acids and their derivatives

 m/c QUIZ on naming RCOOH acids/derivatives * Type in name QUIZ on naming RCOOH acids/derivatives

ACID ANHYDRIDES

 …OIC ANHYDRIDE e.g. CARBOXYLIC ACID ANHYDRIDES with the RCO-O-RCO linkage e.g.

orethanoic anhydride

orpentanoic anhydride

Exemplar homologous series: (C_nH_2n+1CO)₂O derived from aliphatic mono carboxylic acids (n=2,3 etc.)

further Notes and examples of the structure and nomenclature of carboxylic acids and their derivatives

m/c QUIZ on naming RCOOH acids/derivatives * Type in name QUIZ on naming RCOOH acids/derivatives

ACID or ACYL CHLORIDES

 …OYL CHLORIDE e.g. CARBOXYLIC ACID or ACYL CHLORIDES with the -COCl functional group e.g.

orpropanoyl chloride, butanoyl chloride

orpentanoyl chloride,benzoyl chloride

Exemplar homologous series: C_nH_2n+1COCl derived from aliphatic mono carboxylic acid chlorides (n=1,2,3 etc.)

further Notes and examples of the structure and nomenclature of carboxylic acids and their derivatives

m/c QUIZ on naming RCOOH acids/derivatives * Type in name QUIZ on naming RCOOH acids/derivatives

Notes on selected reactions of acid/acyl chlorides from a mechanistic point of view but giving general equations and reaction conditions too

ACID AMIDES

 …AMIDE e.g. CARBOXYLIC ACID AMIDES with the -CONH₂ functional group e.g.

orethanamide,propanamide

butanamide,pentanamide,benzamide

Exemplar homologous series: C_nH_2n+1CONH₂ derived from aliphatic mono carboxylic acid amides (n=0,1,2,3 etc.)

further Notes and examples of the structure and nomenclature of carboxylic acids and their derivatives

and also other organic nitrogen compounds

m/c QUIZ on naming RCOOH acids/derivatives * Type in name QUIZ on naming RCOOH acids/derivatives

ESTERS

 alkyl/aryl …OATE e.g. ESTERS of CARBOXYLIC ACIDS derived from ALCOHOLS or PHENOLS.

Esters have the -COOC- linkage:

methyl methanoate,  propyl propanoate

ethyl propanoate,  ethyl benzoate

Exemplar homologous series: C_xH_2x+1-COO-C_yH_2y+1 simple saturated aliphatic esters (x=0,1,2, etc. and y=1,2,3 etc.)

or the less informative C_nH_2nO₂ (n=2,3,4 etc.) isomeric with carboxylic acids

further Notes and examples of the structure and nomenclature of carboxylic acids and their derivatives

m/c QUIZ on naming RCOOH acids/derivatives * Type in name QUIZ on naming RCOOH acids/derivatives

NITRILES

The nitrile functional group consists of a carbon to nitrogen triple bond.

The name is based on the longest carbon chain, including the C of the nitrile group e.g.

methanenitrile, , ,

ethanenitrile, , , , , ,

propanenitrile, , , , , ,

Exemplar homologous series: C_nH_2n+1CN derived from aliphatic mono carboxylic acid chlorides (n=0,1,2,3 etc.)

further Notes and examples of the structure and nomenclature of carboxylic acids and their derivatives

and also other organic nitrogen compounds

AMINES

PRIMARY AMINES have two hydrogen atoms and one alkyl or aryl group attached to the nitrogen to form the amine or amino group -NH₂.

ALIPHATIC: methylamine (aminomethane), , , ,

ethylamine (aminoethane), , , ,

Exemplar homologous series: C_nH_2n+1NH₂ for saturated mono primary amines (n=1,2,3 etc.)

SECONDARY AMINES have one hydrogen atom and two alkyl or aryl groups attached to the nitrogen

ALIPHATIC: dimethylamine, ,,

ethylmethylamine, ,

diethylamine, ,

TERTIARY AMINES have no hydrogen atom and three alkyl or aryl groups attached to the nitrogen

ALIPHATIC: trimethylamine, ,

ethyldimethylamine, ,

diethylmethylamine, ,

further examples of the structure and nomenclature of organic nitrogen compounds

QUATERNARY AMMONIUM SALTS

If all for hydrogens of an ammonium ion are replaced with alkyl or aryl groups then an ionic quaternary salt is formed.

e.g. the simplest is tetramethylammonium chloride, (CH₃)₄N⁺ Cl^-

NITRO-AROMATIC COMPOUNDS

These have the nitro -NO₂ group directly attached to the ring e.g.

2-methylnitrobenzene or 1-methyl-2-nitrobenzene,

and also other organic nitrogen compounds

DIAZONIUM SALTS and AZO DYES

Diazonium salts are formed when primary aromatic amines reaction with nitrous acid

The diazonium cation has a nitrogen - nitrogen triple bond system directly attached to the benzene ring e.g.

(1) from phenylamine+

(2) from 4-methylphenylamine

In alkaline solution these diazonium salts couple with phenols and aromatic amines to form azo dyes which have benzene rings linked with an azo -N=N- bond system e.g.

reacting (1) with phenol gives

reacting (2) with phenylamine gives

and also other organic nitrogen compounds

These molecules have a strongly mono-basic acidic group -SO₂OH directly attached to the benzene ring e.g.

2-, 3- or 4-methylbenzenesulphonic acid,, , (or ....sulfonic acid)