methylbenzene (toluene) C₇H₈, C₆H₅CH₃

ethylbenzeneC₈H₁₀ and propylbenzene

phenylethene ('styrene'), C₈H₈, is named as a derivative of ethene,

the C₆H₅- aromatic ring grouping is called a phenyl group when quoted as a substituent  prefix.

So phenylethene is named as a derivative of ethene.

1,2-dimethylbenzene, C₈H₁₀, , 1,3-dimethylbenzene, 1,4-dimethylbenzene

(once called xylenes, ortho, meta and para-xylene)

1-ethyl-2-methylbenzene, C₉H₁₂, and the two other positional structural isomers

1-ethyl-3-methylbenzene, C₉H₁₂, and

1-methyl-2-propylbenzene, C₁₀H₁₄, and the two other positional structural isomers

1-methyl-3-propylbenzene, C₁₀H₁₄,and

4-ethyl-1,2-dimethylbenzene, C₁₀H₁₄, (uses lower numbers than 1-...-3,4-...)

Examples of fused ring systems of arene hydrocarbon compounds - polynuclear aromatic ring compounds

Two aromatic rings that share a pair of carbon atoms are said to be fused. These molecules behave exactly like benzene in their chemistry i.e. they display the typical aromaticity of the single ring arenes above in undergoing electrophilic substitution reactions.

naphthalene , C₁₀H₈  consists of two fused aromatic rings

anthracene or  C₁₄H₁₀  consists of three fused rings.

Naphthalene and anthracene are two of the simplest examples of what are called polynuclear aromatic compounds or in this specific case polycyclic aromatic hydrocarbons (PAHs), also known as polycyclic arenes or polyaromatic hydrocarbons. They are molecules which consist of at least two 'benzene' rings 'fused' together. Incidentally the ultimate molecule with this carbon based aromatic ring system is graphene (essentially an individual layer of graphite!)

Both naphthalene and anthracene are correctly shown in Kekule style skeletal formula here (principal IUPAC accepted style), though some textbooks consider drawing molecules like naphthalene in the following style ...

and are considered as incorrect because, although both rings involve delocalised pi electron systems, and, they are both merged into a continuous delocalised pi electron system, this style of diagram implies two separate delocalised ring systems, which is incorrect. However, some undergraduate textbooks and high school textbooks use the 'multi-inner circle' style of skeletal formula. BUT such a style, also implies for the 'inner' vertical C-C bonds (as drawn above between rings), that they are equivalent to a double bond (bond order 2), but each C-C bond in the rings has an average bond order of 1.5 in the delocalised aromatic ring system. Although beyond the scope of this site, anthracene (naphthalene?) does show some ready addition reactions characteristic of a non-aromatic diene!

OLYMPICENE molecular structure, shape and bond angles

Olympicene (caught my imagination in 2012!), C₁₉H₁₂, (M_r = 240, bpt 512^oC), was one of the latest arrivals of a polynuclear aromatic hydrocarbon compound from synthetic organic chemistry in 2011. It was conceived and synthesised by a British research group for the London 2012 Olympic Games. The Olympicene molecule consists of five 'fused' hexagonal rings of carbon atoms (the official Olympic symbol consists of five 'interlocking rings' - can't show due to copyright law!).

Consisting of five shared-fused hexagonal carbon atom rings, Olympicene is a 'flat' or planar molecule (if you ignore the H atoms of the saturated -CH₂- which will 'stick out' above/below the planarity of the molecule). In Olympicene, four of the hexagonal carbon atom rings are truly aromatic rings with C-C-C and C-C-H bond angles of ~120^o. However, due to valence bond limitations, (in left-hand representation), one of the carbon atoms of the bottom-right ring, must be saturated with two hydrogen atoms (shown in diagram). This means in the delocalised system of '4²/₃' rings there are 18 delocalised pi electrons NOT 19 in Olympicene. In the 2nd isomer shown (on the right), the saturated carbon atom is at the top of the top middle ring. This means these cases the H-C-H bond angle of the saturated carbon will be between 109^o and 120^o (probably around 115^o?). What is shown in the above diagram are two of the many possible isomeric 'Kekule' skeletal formula structures. You can write more structures of Olympicene in a similar manner eg put the saturated carbon in one of three positions (a sort of 1, 2 or 3 position) in the top right hexagonal carbon ring, or on the bottom carbon atom of one of the lower rings - try this exercise out and let me know how you get on! am I right, that there are six structural isomers? I'm not exactly sure what isomers were actually produced in the synthesis of Olympicene? and I'm not sure if there is a dynamic equilibrium between two or more of the isomers, though going from one isomer to another involves a proton migration from a strong C-H bond?

Halo-arenes - aryl/aromatic 'halides'

or aryl halide, aromatic halogen compounds, the halogen is directly attached to the benzene ring.

chlorobenzene, C₆H₅Cl, and

1,2 or 1,3 or 1,4-dichlorobenzene, C₆H₄Cl₂, ,,

C₇H₇Cl, chloromethylbenzene, or (chloromethyl)benzene (benzyl chloride). It is not a true aryl halogen compound, the halogen atom is in a non-aromatic side chain, so it is a primary aliphatic halogenoalkane.

Three positional structural isomers of C₇H₇Cl

chloro-2-methylbenzene, chloro-3-methylbenzene and chloro-4-methylbenzene,or 1-chloro-2-methylbenzene, 1-chloro-3-methylbenzene and 1-chloro-4-methylbenzene (old names 0-chlorotoluene, m-chlorotoluene and p-chlorotoluene). These are true aryl halides with the halogen attached directly to the benzene ring and they are isomeric with (chloromethyl)benzene above.

C₇H₆Cl₂, 2,3-dichloromethylbenzene and

C₈H₉Cl, 1-chloro-2,4-dimethylbenzene

This difference is illustrated below with molecules containing a benzene ring (Phenols ROH, R=aryl only)

Phenols form salts with strong bases e.g. the alkali sodium hydroxide gives ....

sodium phenoxide (old name sodium phenate?)

  C₆H₅OCl, 2-chlorophenol (o-chlorophenol)

C₇H₈O, 3-methylphenol (m-methylphenol, meta-cresol)

C₆H₇NO,  2-aminophenol, 4-aminophenol and 2-nitrophenol

C₇H₆O₃, 3-hydroxybenzoic acid and 2-hydroxybenzoic acid

C₆H₆O₂, or 1,4-dihydroxybenzene (benzene-1,4-diol, 1,4-benzenediol, 'quinol')

which is oxidised to

C₆H₄O₂, or 2,5-cyclohexadiene-1,4-dione (cycohexa-2,5-diene-1,4-dione, 'p-quinone')

If the OH is not attached to a benzene ring you get an aliphatic alcohol which is isomeric with a phenols or an ether.

C₇H₈O,phenylmethanol (old name 'benzyl alcohol') is a primary aliphatic alcohol

which is isomeric with methylphenols and the ether, methoxybenzene (anisole).

C₈H₁₀O,1-phenylethanol, which is  isomeric with the ether

C₈H₁₀O, ethoxybenzene (phenetole) and the ethylphenols or dimethylphenols.

True aromatic aldehydes, R-CHO, have the aldehyde group -CHO directly attached to the ring e.g.

C₇H₆O, orbenzaldehyde, and

 C₇H₆O₂, 2-hydroxybenzaldehyde

Ketones, R₂C=O, are often 'mixed' aliphatic-aromatic in the sense that one R group is alkyl and the other is aryl e.g.

1-phenylethanone (acetophenone, methyl phenyl ketone), C₈H₈O,  , and C₈H₈O₂,  

Diphenylmethanone (diphenyl ketone), C₁₃H₁₀O, , is a completely aromatic ketone.

Primary AROMATIC amines

(primary, 2 H's and only one R group attached to the N of the amine group, R-NH₂ where R = alkyl or aryl)

The amino (prefix) or amine (suffix) group is directly attached to the aromatic benzene ring

e.g. C₆H₇N, the simplest is C₆H₅NH₂, phenylamine

C₆H₆NCl, 2- or 3- or 4-chlorophenylamine

C₇H₉N, 2-methylphenylamine, methyl-2-phenylamine, 1-amino-2-methylbenzene  or 2-aminomethylbenzene

This is isomeric with benzylamine which is a primary aliphatic amine because the amine group is not directly attached to the ring.

(secondary, one H and two R groups attached to the N of the amine group, R₂NH where R = alkyl or aryl)

C₇H₉N, N-methylphenylamine, and C₈H₁₁N, N-ethylphenylamine

and C₁₀H₁₁N, diphenylamine

(tertiary, no H and three R groups attached to the N of the amine group, R₃N where R = alkyl or aryl)

and C₁₈H₁₅N, triphenylamine

(primary, no alkyl/aryl R group and 2H's on the N of amide group)

The simplest primary aromatic acid amide is

benzamide or benzenecarboxamide, C₇H₇NO,, ,

(secondary, 1 alkyl/aryl R group and 1H on the N of amide group)

N-phenylethanamide, C₈H₉NO, (this is really a phenyl derivative of an aliphatic amide)

N-methylbenzamide, C₈H₉NO,  , and

N-phenylbenzamide, C₁₃H₁₁NO,     (both true secondary aromatic amide)

-COOH + H₂N- ==> -CO-NH- + H₂O

Tertiary amides would have no H and 2 aryl/alkyl groups on N of amide group.

e.g. C₆H₅NH₂(aq) + HNO_2(aq) + H⁺_(aq) ==> C₆H₅N₂⁺_(aq) + 2H₂O_(l)

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

These dyes have benzene rings linked with an azo -N=N- bond system e.g.

C₇H₇NO₂,  methyl-2-nitrobenzene, or 1-methyl-2-nitrobenzene (o-nitrotoluene, ortho nitrotoluene)

and the two other positional structural isomers

methyl-3-nitrobenzene, or 1-methyl-3-nitrobenzene (m-nitrotoluene, meta nitrotoluene)

and

methyl-4-nitrobenzene, or 1-methyl-4-nitrobenzene (p-nitrotoluene, para nitrotoluene)

and a substituted aromatic carboxylic acid, C₇H₅NO₃, 3-nitrobenzoic acid,

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

benzenesulphonic acid, C₆H₆SO₃, C₆H₅SO₃H, C₆H₅SO₂OH, (or benzenesulphonic acid)

2-, 3- or 4-methylbenzenesulfonic acid, C₇H₈SO₃, CH₃C₆H₅SO₂OH,, , 

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

A level 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, WJEC GCE AS A2 Chemistry, CCEA/CEA GCE AS A2 Chemistry revising courses for pre-university students (equal to US grade 11 and grade 12 and AP Honours/honors level courses)

formula keywords: how to name naming nomenclature empirical molecular formula graphic formula displayed formula skeletal formula structural isomers isomerism Hydrocarbons (Arenes) ... Halo-Aromatics ... Phenols ... Aldehydes and Ketones ... Carboxylic Acids and Derivatives ... primary prim secondary sec tertiary tert Amines (prim/sec/tert) ... Amides ... Diazonium Salts and azo dyes ... Nitro-Aromatics ... Sulphonic Acids   C6H6 C7H8 C6H5CH3 C8H10 CH3C6H4CH3 C6H5CH2CH3 C8H18 C6H5CH=CH2 C9H12 C10H14 C11H16 C6H5Cl C6H4Cl2 ClC6H4Cl C7H7Cl C6H5CH2Cl CH3C6H4Cl C7H6Cl2 C8H9Cl C6H6O C6H5OH C6H5OCl C6H5ClO ClC6H4OH C7H8O CH3C6H4OH HOC6H4NH2 NH2C6H4OH H2NC6H4OH C6H7ON C6H7NO C7H6O3 HOC6H4COOH C7H6OCl2 C7H6Cl2O C6H6O2 HOC6H4OH C6H4O2 C6H5CH2OH C6H5OCH3 C8H10O C6H5OCH2CH3 C6H5OCH2CH7H6O2 C6H5COOH C7H6O C6H5CHO C7H6O2 HOC6H4CHO C8H8O C6H5COOCH3 C8H8O2 C13H10O C7H6O2 C6H5COOH C7H5OCl C7H5ClO C68H11N C6H5NHCH2CH3 C6H5COCl C7H7ON C7H7NO C6H5CONH2 C8H8O2 C6H5COOCH3 C8H8O3 C9H10O2 C6H5COOCH2CH3 C9H10O2 C10H12O2 C6H5COOCH2CH2CH3 C7H6O3 HOC6H4COOH C7H5ClO2 C7H5O2Cl ClC6H4COOH C8H6O4 HOOCC6H6COOH C6H7N C6H5NH2 C6H6NCl C6H6ClN C6H8N2 H2NC6H4NH2 NH2C6H4NH2 C7H9N CH3C6H4NH2 C6H5CH2NH2 C6H5NHCH3 C8H11N C6H5NHCH2CH3 C10H11N C6H5NHC6H5 C9H11N C10H15N C18H15N C7H7NO C7H7ON C6H5CONH2 C8H9NO C8H9ON CH3CONHC6H5 C6H5CONHCH3 C13H11NO C13H11ON C6H5CONHC6H5 C9H11NO C9H11ON C6H5NO2 C6H5ON2 C6H4N2O4 C6H4O4N2 C6H4NO2Cl C6H4O2NCl C6H4O2ClN C6H4ClNO2 C6H4ClO2N C6H4NClO2 ClC6H4NO2 O2NC6H4Cl NO2C6H4Cl C7H7NO2 C7H7O2N CH3C6H4NO2 O2NC6H4CH3 NO2C6H4CH3 C7H5NO3 O2NC6H4COOH NO2C6H4COOH C6H6O3S C6H6SO3 C6H5SO3H C6H5SO2OH C7H8SO3 CH3C6H4SO2OH C10H8 C14H10 C19H12

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