Doc Brown's Chemistry
Revising Advanced Level Organic Chemistry
Revision Notes Part 9 FUNCTIONAL GROUPS and HOMOLOGOUS SERIES
A summary guide to the Molecular Structure and Naming-Nomenclature of Functional Groups and Homologous Series in Organic Chemistry
Following an introduction answering the question WHY is there such a range of organic molecules? there are sections of styles of representing the structure of organic molecules e.g. molecular formula and molecular structure. Then 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. Alkanes, Alkenes, Alkynes, Aromatics-arenes, Halogenoalkanes, Alcohols (prim/sec/tert), Phenols, Ethers, Aldehydes, Ketones, Carboxylic acids, Acid/acyl chlorides, Acid Anhydrides, Acid/acyl Amides, Esters, Nitriles, Amines (prim/tert/sec), Quaternary ammonium salts, Nitro-aromatics, Diazonium salts and dyes, Sulphonic (sulfonic) acids and a variety possible Aromatic Compounds and Organic Nitrogen Compounds are also included. At the end is a guide to primary, secondary and tertiary structures i.e. the CLASSIFICATION system for haloalkanes, alcohols, amines and amides.
Page sub-index: INTRODUCTION * 9.1.1 Styles of structure and formula representation * 9.1.2 Alkanes, Alkenes, Alkynes, Aromatics-arenes, Halogenoalkanes, Alcohols (prim/sec/tert), Phenols, Ethers, Aldehydes, Ketones, Carboxylic acids, Acid chlorides, Acid Anhydrides, Amides, Esters, Nitriles, Amines (prim/tert/sec), Quaternary ammonium salts, Nitro-aromatics, Diazonium salts and dyes, Sulphonic (sulfonic) acids, Appendix 1 Guide to primary, secondary and tertiary CLASSIFICATION. More examples, due to the variety of Aromatic Compounds and Organic Nitrogen Compounds, are on separate web pages.
BUT first ... AN INTRODUCTION TO ORGANIC CHEMISTRY i.e. WHY is there such a range of organic molecules and hence why a vast discipline of organic chemistry?
9.1.1 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 displayed formula with full 3D spatial representation e.g. which shows the shape of the molecule and implies bond angles (in this case all are 109o). The 'dotted line' bond is behind the plane of the screen/paper/page and the 'wedge' bond is towards you. The other two thin line bonds are in the plane of the screen/paper/page etc. This gives a good impression of the real shape of the molecule in terms of the directional covalent bonds and all bond angles here are ~109o.
A skeletal formula e.g. in which none of the 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 C-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 CxHyOz etc. where x, y and z are integer 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
CnH2n+2 for alkanes, so that n=1 generates the formula for methane CH4 and n=5 generates the formula for pentane C5H12 etc. and .....
CnH2n+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.
FUNCTIONAL GROUPS and HOMOLOGOUS SERIES
Summary of nomenclature, structure and representation in pictures-graphics
9.1.2 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.) …
Exemplar homologous series: CnH2n+2 for non-cyclo alkanes (n=1,2,3 etc.)
and CnH2n for cycloalkanes (n=3,4,5 etc.) isomeric with non-cyclo alkenes
9.1.3 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 …
Exemplar homologous series: CnH2n for non-cyclo alkenes (n=2,3 etc. with one C=C bond) isomeric with cycloalkanes
and CnH2n-2 for cycloalkenes (n=3,4,5 etc., and with one C=C bond)
9.1.4 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: CnH2n-2 for non-cyclo alkynes (with one triple bond)
9.1.5 AROMATIC HYDROCARBONS (unsaturated)
'ARENES' are aromatic hydrocarbons with at least one benzene ring functional group e.g. …
further Notes and examples of aromatics
9.1.6 aliphatic/aromatic HALOGEN COMPOUNDS
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.
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: CnH2n+1X for non-cyclo saturated halogenoalkanes (X=F,Cl,Br,I and n=1,2,3 etc.)
NOTE: Aromatic HALO ... ARENES (aromatic halogen compounds) have the halogen atom directly attached to the benzene ring.
9.1.7 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
Secondary aliphatic alcohols R-CH(OH)-R' where R or R' are both alkyl (or aryl):
cyclopentanol, 2-hydroxybutanoic acid*
Tertiary aliphatic alcohols RR'R"C-OH where R,R' or R" are all alkyl (or aryl):
Exemplar homologous series: CnH2n+1OH for saturated non-cyclic aliphatic alcohols (n=1,2,3 etc.)
or the less informative CnH2n+2O isomeric with aliphatic non-cyclo ethers
and CnH2n-1OH for cycloalcohols (n=3,4,5 etc. with one C-OH)
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.
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).
Exemplar homologous series: CxH2x+1-O-CyH2y+1 for saturated non-cyclo ethers (x or y =1,2,3 etc.)
or the less informative CnH2n+2O (n=2,3,4 etc.) isomeric with non-cyclo aliphatic alcohols
or CnH2nO for cycloethers (n=2,3,4 etc. with one C-O-C linkage, non shown at the moment)
9.1.9 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.
Exemplar homologous series: CnH2n+1CHO for aliphatic aldehydes (n=0,1,2 etc.)
or the less in formative CmH2mO (m=1,2,3 etc.) isomeric with ketones and saturated cyclic aliphatic ethers
…ONE e.g. KETONES have the C-CO-C functional group linkage within the carbon chain:
Exemplar homologous series: CxHxn+1-CO-CyH2y+1 for aliphatic ketones (x or y = 1,2,3, etc.)
or the less informative CnH2nO (n=3,4,5 etc.) isomeric with aldehydes and saturated cyclic aliphatic ethers
9.1.10 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: CnH2n+1COOH for saturated aliphatic mono carboxylic acids (n=0,1,2,3 etc.)
or the less informative CnH2nO2 (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)
9.1.11 ACID ANHYDRIDES
…OIC ANHYDRIDE e.g. CARBOXYLIC ACID ANHYDRIDES with the RCO-O-RCO linkage e.g.
Exemplar homologous series: (CnH2n+1CO)2O derived from aliphatic mono carboxylic acids (n=2,3 etc.)
…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: CnH2n+1COCl derived from aliphatic mono carboxylic acid chlorides (n=1,2,3 etc.)
9.1.13 ACID AMIDES
…AMIDE e.g. CARBOXYLIC ACID AMIDES with the -CONH2 functional group e.g.
Exemplar homologous series: CnH2n+1CONH2 derived from aliphatic mono carboxylic acid amides (n=0,1,2,3 etc.)
and also other organic nitrogen compounds
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: CxH2x+1-COO-CyH2y+1 simple saturated aliphatic esters (x=0,1,2, etc. and y=1,2,3 etc.)
or the less informative CnH2nO2 (n=2,3,4 etc.) isomeric with carboxylic acids
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: CnH2n+1CN derived from aliphatic mono carboxylic acid chlorides (n=0,1,2,3 etc.)
and also other organic nitrogen compounds
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: CnH2n+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, ,,
TERTIARY AMINES have no hydrogen atom and three alkyl or aryl groups attached to the nitrogen
ALIPHATIC: trimethylamine, ,
9.1.17 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-
9.1.18 NITRO-AROMATIC COMPOUNDS
These have the nitro -NO2 group directly attached to the ring e.g.
nitrobenzene, ; 1,3-dinitrobenzene,
2-methylnitrobenzene or 1-methyl-2-nitrobenzene,
and also other organic nitrogen compounds
9.1.19 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
9.1.20 SULPHONIC ACIDS
These molecules have a strongly mono-basic acidic group -SO2OH directly attached to the benzene ring e.g.
benzenesulphonic acid, ,(or benzenesulfonic acid)
2-, 3- or 4-methylbenzenesulphonic acid,, , (or ....sulfonic acid)
APPENDIX 1 A guide to primary, secondary and tertiary structures
The CLASSIFICATION system for haloalkanes, alcohols, amines and amides
LINKS TO OTHER ASSOCIATED PAGES
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