function mOver(colour){
colour.style.color="yellow"
}

function mOut(colour){
colour.style.color="crimson"
}

function alkanes(x){
if (x.className=="dark") x.className="light"
//alkane.className="dark"
alkene.className="dark"
alkyne.className="dark"
halogenoalkane.className="dark"
alcohol.className="dark"
ether.className="dark"
amine.className="dark"
nitrile.className="dark"
aldehyde.className="dark"
ketone.className="dark"
carboxylic.className="dark"
acidchloride.className="dark"
amide.className="dark"
ester.className="dark"
acidanhydride.className="dark"
benzene.className="dark"
phg.className="dark"
}

function alkenes(x){
if (x.className=="dark") x.className="light"
alkane.className="dark"
//alkene.className="dark"
alkyne.className="dark"
halogenoalkane.className="dark"
alcohol.className="dark"
ether.className="dark"
amine.className="dark"
nitrile.className="dark"
aldehyde.className="dark"
ketone.className="dark"
carboxylic.className="dark"
acidchloride.className="dark"
amide.className="dark"
ester.className="dark"
acidanhydride.className="dark"
benzene.className="dark"
phg.className="dark"
}

function alkynes(x){
if (x.className=="dark") x.className="light"
alkane.className="dark"
alkene.className="dark"
//alkyne.className="dark"
halogenoalkane.className="dark"
alcohol.className="dark"
ether.className="dark"
amine.className="dark"
nitrile.className="dark"
aldehyde.className="dark"
ketone.className="dark"
carboxylic.className="dark"
acidchloride.className="dark"
amide.className="dark"
ester.className="dark"
acidanhydride.className="dark"
benzene.className="dark"
phg.className="dark"
}

function halogenoalkanes(x){
if (x.className=="dark") x.className="light"
alkane.className="dark"
alkene.className="dark"
alkyne.className="dark"
//halogenoalkane.className="dark"
alcohol.className="dark"
ether.className="dark"
amine.className="dark"
nitrile.className="dark"
aldehyde.className="dark"
ketone.className="dark"
carboxylic.className="dark"
acidchloride.className="dark"
amide.className="dark"
ester.className="dark"
acidanhydride.className="dark"
benzene.className="dark"
phg.className="dark"
}

function alcohols(x){
if (x.className=="dark") x.className="light"
alkane.className="dark"
alkene.className="dark"
alkyne.className="dark"
halogenoalkane.className="dark"
//alcohol.className="dark"
ether.className="dark"
amine.className="dark"
nitrile.className="dark"
aldehyde.className="dark"
ketone.className="dark"
carboxylic.className="dark"
acidchloride.className="dark"
amide.className="dark"
ester.className="dark"
acidanhydride.className="dark"
benzene.className="dark"
phg.className="dark"
}

function ethers(x){
if (x.className=="dark") x.className="light"
alkane.className="dark"
alkene.className="dark"
alkyne.className="dark"
halogenoalkane.className="dark"
alcohol.className="dark"
//ether.className="dark"
amine.className="dark"
nitrile.className="dark"
aldehyde.className="dark"
ketone.className="dark"
carboxylic.className="dark"
acidchloride.className="dark"
amide.className="dark"
ester.className="dark"
acidanhydride.className="dark"
benzene.className="dark"
phg.className="dark"
}

function amines(x){
if (x.className=="dark") x.className="light"
alkane.className="dark"
alkene.className="dark"
alkyne.className="dark"
halogenoalkane.className="dark"
alcohol.className="dark"
ether.className="dark"
//amine.className="dark"
nitrile.className="dark"
aldehyde.className="dark"
ketone.className="dark"
carboxylic.className="dark"
acidchloride.className="dark"
amide.className="dark"
ester.className="dark"
acidanhydride.className="dark"
benzene.className="dark"
phg.className="dark"
}

function nitriles(x){
if (x.className=="dark") x.className="light"
alkane.className="dark"
alkene.className="dark"
alkyne.className="dark"
halogenoalkane.className="dark"
alcohol.className="dark"
ether.className="dark"
amine.className="dark"
//nitrile.className="dark"
aldehyde.className="dark"
ketone.className="dark"
carboxylic.className="dark"
acidchloride.className="dark"
amide.className="dark"
ester.className="dark"
acidanhydride.className="dark"
benzene.className="dark"
phg.className="dark"
}

function aldehydes(x){
if (x.className=="dark") x.className="light"
alkane.className="dark"
alkene.className="dark"
alkyne.className="dark"
halogenoalkane.className="dark"
alcohol.className="dark"
ether.className="dark"
amine.className="dark"
nitrile.className="dark"
//aldehyde.className="dark"
ketone.className="dark"
carboxylic.className="dark"
acidchloride.className="dark"
amide.className="dark"
ester.className="dark"
acidanhydride.className="dark"
benzene.className="dark"
phg.className="dark"
}

function ketones(x){
if (x.className=="dark") x.className="light"
alkane.className="dark"
alkene.className="dark"
alkyne.className="dark"
halogenoalkane.className="dark"
alcohol.className="dark"
ether.className="dark"
amine.className="dark"
nitrile.className="dark"
aldehyde.className="dark"
//ketone.className="dark"
carboxylic.className="dark"
acidchloride.className="dark"
amide.className="dark"
ester.className="dark"
acidanhydride.className="dark"
benzene.className="dark"
phg.className="dark"
}

function carboxylics(x){
if (x.className=="dark") x.className="light"
alkane.className="dark"
alkene.className="dark"
alkyne.className="dark"
halogenoalkane.className="dark"
alcohol.className="dark"
ether.className="dark"
amine.className="dark"
nitrile.className="dark"
aldehyde.className="dark"
ketone.className="dark"
//carboxylic.className="dark"
acidchloride.className="dark"
amide.className="dark"
ester.className="dark"
acidanhydride.className="dark"
benzene.className="dark"
phg.className="dark"
}

function acidchlorides(x){
if (x.className=="dark") x.className="light"
alkane.className="dark"
alkene.className="dark"
alkyne.className="dark"
halogenoalkane.className="dark"
alcohol.className="dark"
ether.className="dark"
amine.className="dark"
nitrile.className="dark"
aldehyde.className="dark"
ketone.className="dark"
carboxylic.className="dark"
//acidchloride.className="dark"
amide.className="dark"
ester.className="dark"
acidanhydride.className="dark"
benzene.className="dark"
phg.className="dark"
}

function amides(x){
if (x.className=="dark") x.className="light"
alkane.className="dark"
alkene.className="dark"
alkyne.className="dark"
halogenoalkane.className="dark"
alcohol.className="dark"
ether.className="dark"
amine.className="dark"
nitrile.className="dark"
aldehyde.className="dark"
ketone.className="dark"
carboxylic.className="dark"
acidchloride.className="dark"
//amide.className="dark"
ester.className="dark"
acidanhydride.className="dark"
benzene.className="dark"
phg.className="dark"
}

function esters(x){
if (x.className=="dark") x.className="light"
alkane.className="dark"
alkene.className="dark"
alkyne.className="dark"
halogenoalkane.className="dark"
alcohol.className="dark"
ether.className="dark"
amine.className="dark"
nitrile.className="dark"
aldehyde.className="dark"
ketone.className="dark"
carboxylic.className="dark"
acidchloride.className="dark"
amide.className="dark"
//ester.className="dark"
acidanhydride.className="dark"
benzene.className="dark"
phg.className="dark"
}

function acidanhydrides(x){
if (x.className=="dark") x.className="light"
alkane.className="dark"
alkene.className="dark"
alkyne.className="dark"
halogenoalkane.className="dark"
alcohol.className="dark"
ether.className="dark"
amine.className="dark"
nitrile.className="dark"
aldehyde.className="dark"
ketone.className="dark"
carboxylic.className="dark"
acidchloride.className="dark"
amide.className="dark"
ester.className="dark"
//acidanhydride.className="dark"
benzene.className="dark"
phg.className="dark"
}

function benzenes(x){
if (x.className=="dark") x.className="light"
alkane.className="dark"
alkene.className="dark"
alkyne.className="dark"
halogenoalkane.className="dark"
alcohol.className="dark"
ether.className="dark"
amine.className="dark"
nitrile.className="dark"
aldehyde.className="dark"
ketone.className="dark"
carboxylic.className="dark"
acidchloride.className="dark"
amide.className="dark"
ester.className="dark"
acidanhydride.className="dark"
//benzene.className="dark"
phg.className="dark"
}

function aromatics(x){
if (x.className=="dark") x.className="light"
alkane.className="dark"
alkene.className="dark"
alkyne.className="dark"
halogenoalkane.className="dark"
alcohol.className="dark"
ether.className="dark"
amine.className="dark"
nitrile.className="dark"
aldehyde.className="dark"
ketone.className="dark"
carboxylic.className="dark"
acidchloride.className="dark"
amide.className="dark"
ester.className="dark"
acidanhydride.className="dark"
benzene.className="dark"
//phg.className="dark"
}

function cAlkane(){
content.innerHTML="<P><B>Hydrocarbons</B> are compounds containing the elements carbon and hydrogen only. There are three aliphatic series: <B>Alkanes</B>, <B>Alkenes</B>, and <B>Alkynes</B>.<P>The <B>Alkanes</B> are a series of <I>saturated</I> hydrocarbons characterised by carbon-carbon single bonds. They have the general formula <B>C<SUB>n</SUB>H<SUB>2n+2</SUB></B>, where n = 1,2,3,4, etc. and is the number of carbon atoms in the molecule. The first member of the series, <B>methane</B>, has a formula CH<SUB>4</SUB> (n = 1), followed by <B>ethane</B>, C<SUB>2</SUB>H<SUB>6</SUB> (n = 2), <B>propane</B>, C<SUB>3</SUB>H<SUB>8</SUB> (n = 3), and so on.<P>Each of the above molecular formulae can be represented by only one structural formula. Where n = 4, the molecular formula is C<SUB>4</SUB>H<SUB>10</SUB>. This can be represented by two different structural formulae: the straight-chain isomer <B>butane</B>, CH<SUB>3</SUB>CH<SUB>2</SUB>CH<SUB>2</SUB>CH<SUB>3</SUB>, and the branched isomer, <B>methlypropane</B>, CH<SUB>3</SUB>CHCH<SUB>3</SUB>CH<SUB>3</SUB>. <I>Structural isomers</I> have the same molecular formula but different structural formulae.<P><CENTER><IMG SRC=c4h10.gif WIDTH=300 HEIGHT=133></CENTER>"
}

function cAlkene(){
content.innerHTML="<P>The <B>Alkenes</B> are a series of <I>unsaturated</I> hydrocarbons characterised by carbon-carbon double bonds. They have the general formula <B>C<SUB>n</SUB>H<SUB>2n</SUB></B>, where n = 2,3,4, etc. and is the number of carbon atoms in the molecule. The first member of the series is <B>ethene</B>, C<SUB>2</SUB>H<SUB>4</SUB> (n = 2). This can also be written as CH<SUB>2</SUB>CH<SUB>2</SUB>, or as CH<SUB>2</SUB>=CH<SUB>2</SUB> showing the double bond. The second member is <B>propene</B>, C<SUB>3</SUB>H<SUB>6</SUB>, or CH<SUB>3</SUB>CHCH<SUB>2</SUB> (n = 3).<P><CENTER><IMG SRC=ethenepropene.gif WIDTH=250 HEIGHT=80></CENTER><P>Where n = 4, the molecular formula is C<SUB>4</SUB>H<SUB>8</SUB>. This can be represented by three different structural formulae: CH<SUB>2</SUB>=CHCH<SUB>2</SUB>CH<SUB>3</SUB> which is <B>but-1-ene</B>, CH<SUB>3</SUB>CH=CHCH<SUB>3</SUB> which is <B>but-2-ene</B>, and CH<SUB>3</SUB>C(CH<SUB>3</SUB>)=CH<SUB>2</SUB> which is <B>methylpropene</B>. The carbon-carbon double bond allows <B>no</B> free rotation. For this reason, two different molecular models can be constructed for but-2-ene. These models (molecules) cannot be <I>superimposed</I> one upon the other. They must therefore be isomers, but <B>not</B> structural isomers because they have the same structure and bond sequence. They cannot be superimposed because their atoms are orientated differently is space. Such isomers are called <B>stereoisomers</B>. This particular kind of stereoisomerism is called <B>geometric isomerism</B>. The two isomers concerned are <I>cis</I>-but-2-ene and <I>trans</I>-but-2-ene.<P><CENTER><IMG SRC=cistrans.gif WIDTH=450 HEIGHT=107></CENTER>"
}

function cAlkyne(){
content.innerHTML="<P>The <B>Alkynes</B> are a series of <I>unsaturated</I> hydrocarbons characterised by carbon-carbon triple bonds. They have the general formula <B>C<SUB>n</SUB>H<SUB>2n-2</SUB></B>, where n = 2,3,4, etc. and is the number of carbon atoms in the molecule. The first member of the series is <B>ethyne</B>, C<SUB>2</SUB>H<SUB>2</SUB>, or H-C<FONT FACE=Symbol>&#0186;</FONT>C-H (n = 2). <B>Propyne</B> is the second member, C<SUB>3</SUB>H<SUB>4</SUB>, or CH<SUB>3</SUB>-C<FONT FACE=Symbol>&#0186;</FONT>C-H (n = 3).<P><CENTER><IMG SRC=ethynepropyne.gif WIDTH=375 HEIGHT=81></CENTER>"
}

function cHalogenoalkane(){
content.innerHTML="<P><B>Halogenoalkanes</B> are formed in theory by removing an H atom from an alkane and replacing it with a halogen atom (X). The general formula is <B>C<SUB>n</SUB>H<SUB>2n+1</SUB>-X</B>, or <B>R-X</B>, where n = 1,2,3,4, etc. <B>Bromoethane</B>, CH<SUB>3</SUB>CH<SUB>2</SUB>Br (n = 2) is an example. Where n = 3, the molecular formula is, for example, C<SUB>3</SUB>H<SUB>7</SUB>Br. This could represent the two structural isomers: 1-bromopropane and 2-bromopropane.<P><CENTER><IMG SRC=bromopropanes.gif WIDTH=425 HEIGHT=81></CENTER><P>Where n = 4, the molecular formula is, for example, C<SUB>4</SUB>H<SUB>9</SUB>Br. One of the possible structural formulae which this represents is CH<SUB>3</SUB>CHBrCH<SUB>2</SUB>CH<SUB>3</SUB>. This structure provides an example of another kind of <B>stereoisomerism</B> called <B>optical isomerism</B>. The carbon atom to which the bromine is attached has four different atoms or groups of atoms bonded to it.<P><CENTER><IMG SRC=optical.gif WIDTH=410 HEIGHT=124></CENTER><P>Halogenoalkanes can be classified as <B>primary</B>, <B>secondary</B>, or <B>tertiary</B>. This depends upon the number of H atoms <I>attached</I> to the carbon atom to which the halogen atom is bonded. If there are two H atoms (and one alkyl group), then the structure is a primary halogenoalkane, as in bromobutane. Where there is only one H atom (and two alkyl groups) the halogenoalkane is a secondary; no H atoms (and three alkyl groups) the halogenoalkane is a tertiary.<P><CENTER><IMG SRC=pst_rx.gif WIDTH=350 HEIGHT=236></CENTER>"
}

function cAlcohol(){
content.innerHTML="<P><B>Alcohols</B> are formed in theory by removing an H atom from an alkane and replacing it with an -OH group. The general formula is <B>C<SUB>n</SUB>H<SUB>2n+1</SUB>-OH</B>, or <B>R-OH</B>, where n = 1,2,3,4, etc. <B>Ethanol</B>, CH<SUB>3</SUB>CH<SUB>2</SUB>OH (n = 2) is an example. <B>Dihydric alcohols</B> have two -OH groups in the one molecule, for example, <B>ethan-1,2-diol</B>, HOCH<SUB>2</SUB>CH<SUB>2</SUB>OH. Alcohols can be <B>classified</B> as <I>primary</I>, <I>secondary</I>, or <I>tertiary</I>, as for halogenoalkanes.<P><CENTER><IMG SRC=monodiol.gif WIDTH=450 HEIGHT=81></CENTER>"
}

function cEther(){
content.innerHTML="<P><B>Ethers</B> have the general formula <B>C<SUB>n</SUB>H<SUB>2n+1</SUB>-O-C<SUB>n</SUB>H<SUB>2n+1</SUB></B>, or <B>R-O-R'</B>, where n = 1,2,3,4, etc. That is, two alkyl groups bridged by an oxygen atom. n need not have the same value in each alkyl group, or R and R' are the same or different. <B>Ethoxyethane</B>, CH<SUB>3</SUB>CH<SUB>2</SUB>-O-CH<SUB>2</SUB>CH<SUB>3</SUB> (n = 2) is an example.<P><CENTER><IMG SRC=ethoxyethane.gif WIDTH=290 HEIGHT=83></CENTER>"
}

function cAmine(){
content.innerHTML="<P><B>Amines</B> can be thought of as derivatives of ammonia, NH<SUB>3</SUB>. Alkyl groups replace one or two or all three of the H atoms. Amines are classified as <B>primary</B>, <B>secondary</B>, or <B>tertiary</B>, according to the number of H atoms replaced by alkyl groups. Primary amines contain the -NH<SUB>2</SUB> group. They have the general formula, <B>C<SUB>n</SUB>H<SUB>2n+1</SUB>-NH<SUB>2</SUB></B>, or <B>R-NH<SUB>2</SUB></B>, where n = 1,2,3,4, etc. An example is <B>ethylamine</B>, CH<SUB>3</SUB>CH<SUB>2</SUB>-NH<SUB>2</SUB> (n = 2). RR'NH and RR'R''N represent secondary and tertiary amines respectively, where R, R' and R'' are the same or different.<P><CENTER><IMG SRC=amines.gif WIDTH=550 HEIGHT=111></CENTER></P>"
}

function cNitrile(){
content.innerHTML="<P><B>Nitriles</B> are also known as cyanides. They have the general formula <B>C<SUB>n</SUB>H<SUB>2n+1</SUB>-C<FONT FACE=Symbol>&#0186;</FONT>N</B>, where n = 1,2,3,4, etc. <B>Propanenitrile</B>, CH<SUB>3</SUB>CH<SUB>2</SUB>-C<FONT FACE=Symbol>&#0186;</FONT>N (n = 2) is an example.<P><CENTER><IMG SRC=propanenitrile.gif WIDTH=175 HEIGHT=76></CENTER></P>"
}

function cCarbonyl(){
content.innerHTML="<P><B>Carbonyl compounds</B> contain the <I>carbonyl group</I>, >C=O. Two homologous series contain this group: <B>Aldehydes</B> and <B>Ketones</B>. Both have the general formula <B>C<SUB>n</SUB>H<SUB>2n+1</SUB>-CO-C<SUB>n</SUB>H<SUB>2n+1</SUB></B>. <P>However, for <B>aldehydes</B>, n must always be equal to zero in at least one of the alkyl groups. If the general formula is represented as RCHO, then R could be H. The first member of the aldehyde series is <B>methanal</B>, HCHO, (n = 0). <B>Ethanal</B> is the second member, CH<SUB>3</SUB>CHO (n = 1).<P><CENTER><IMG SRC=aldehydes.gif WIDTH=250 HEIGHT=73></CENTER><P>For <B>ketones</B>, n must be equal to at least one in both alkyl groups. The general formula could be represented as R-CO-R', where R and R' are the same or different. The first member of the ketone series is <B>propanone</B>, CH<SUB>3</SUB>COCH<SUB>3</SUB> (n = 1).<P><CENTER><IMG SRC=propanone.gif WIDTH=150 HEIGHT=71></CENTER></P>"
}

function cCarboxyl(){
content.innerHTML="<P><B>Carboxylic Acids</B> contain the <I>carboxyl group</I>, -COOH. They have the general formula <B>C<SUB>n</SUB>H<SUB>2n+1</SUB>-COOH</B>, or <B>R-COOH</B>, where the value of n can be zero, or R can be H. The first member of the series is <B>methanoic acid</B>, HCOOH (n = 0). The second member is <B>ethanoic acid</B>, CH<SUB>3</SUB>COOH (n = 1).<P><CENTER><IMG SRC=acids.gif WIDTH=350 HEIGHT=79></CENTER><P><B>Derivatives of carboxylic acids</B> are obtained in theory by removing the -OH from the carboxyl group and replacing it with another group. They have the general formula <B>C<SUB>n</SUB>H<SUB>2n+1</SUB>-G</B>, where -G is the group that replaces the -OH.<BR><B>Acid Chlorides</B>, <B>Amides</B>, <B>Esters</B>, and <B>Acid Anhydrides</B> are examples."
}

function cAcidCl(){
content.innerHTML="<P><B>Acid Chlorides</B> (Acyl Chlorides) have the general formula C<SUB>n</SUB>H<SUB>2n+1</SUB>CO-Cl (or RCOCl) where n = 1,2,3,4, etc. Replace the -OH of a carboxylic acid with -Cl. <B>Ethanoyl Chloride</B> CH<SUB>3</SUB>COCl (n = 1) is and example.<P><CENTER><IMG SRC=ethanoylcl.gif WIDTH=135 HEIGHT=76></CENTER>"
}

function cAmide(){
content.innerHTML="<P>Two classifications, <B>primary</B> and <B>secondary</B> amides, are encountered at advanced level. They contain the <B>amide linkage</B>, -CONH-.<P><CENTER><IMG SRC=amidelink.gif WIDTH=125 HEIGHT=81></CENTER><P><B>Primary amides</B> have the general formula C<SUB>n</SUB>H<SUB>2n+1CO</SUB>-NH<SUB>2</SUB> (or RCONH<SUB>2</SUB>) where n = 1,2,3,4, etc. An example of a primary amide is <B>ethanamide</B>, CH<SUB>3</SUB>CONH<SUB>2</SUB> (n = 1). Replace the -OH  of a carboxylic acid with -CONH<SUB>2</SUB>. <B>N-methylethanamide</B>, CH<SUB>3</SUB>CONHCH<SUB>3</SUB>, is an example of a <B>secondary amide</B>. The general formula is perhaps best written as RCONHR', where R and R' are the same or different. The secondary amide grouping (-CONH-) occurs in proteins and synthetic polymers such as nylon. Amides can also be thought of as monoacyl derivatives of ammonia.<P><CENTER><IMG SRC=amides.gif WIDTH=450 HEIGHT=94></CENTER>"
}

function cEster(){
content.innerHTML="<P><B>Esters</B> contain the <B>ester linkage</B> (-COO-) in their molecules. Replace the -OH of a carboxylic acid with -OR. <P><CENTER><IMG SRC=esterlink.gif WIDTH=125 HEIGHT=81></CENTER><P>They have the general formula C<SUB>n</SUB>H<SUB>2n+1</SUB>-COO-C<SUB>n</SUB>H<SUB>2n+1</SUB>, or R-COO-R'. R and R' can be the same or different. In this representation, R- can be H- (n = 0), but R'- must always be an alkyl group (n = 1 or more). <B>Methly methanoate</B>, H-COO-CH<SUB>3</SUB> (n = 0, n = 1) and <B>Ethyl ethanoate</B>, CH<SUB>3</SUB>-COO-CH<SUB>2</SUB>CH<SUB>3</SUB> are examples.<P><CENTER><IMG SRC=esters.gif WIDTH=425 HEIGHT=71></CENTER>"
}

function cAcidAnh(){
content.innerHTML="<P><B>Acid Anhydrides</B> have the general formula C<SUB>n</SUB>H<SUB>2n+1</SUB>-CO-O-CO-C<SUB>n</SUB>H<SUB>2n+1</SUB> where n = 1,2,3,4, etc., (or R-CO-O-CO-R' where R and R' are the same or different). Replace the -OH of a carboxylic acid with -OCOR'. A common example is <B>ethanoic anhydride</B>, CH<SUB>3</SUB>-CO-O-CO-CH<SUB>3</SUB> (n = 1).<P><CENTER><IMG SRC=ethanoicanhydride.gif WIDTH=225 HEIGHT=70></CENTER><P>These are compounds in which a water molecule is eliminated between two carboxylic acid molecules. Methanoic acid is exceptional in that it yields carbon monoxide on dehyration, that is, n cannot have the value zero."
}

function cBenzene(){
content.innerHTML="<P><B>Benzene</B>, C<SUB>6</SUB>H<SUB>6</SUB>, is a thin, colourless liquid (b.p., 80.2 <FONT FACE=Symbol>&#0176;</FONT>C) with a characteristic smell. It is highly flammable, burning with a smoky yellow flame. It has been linked with causing cancer and its use is very restricted.<P>Benzene was first isolated by Faraday in 1825 from the liquid condensed by compressing oil gas. Most benzene is now manufactured from suitable petroleum fractions. Its principal industrial use is as a starting point for other chemicals, particularly styrene, phenol and nylon.<P>That carbon can single bond to four other atoms and also form double and triple bonds was recognised by <B>Kekul&#0233;</B> in 1858. Numerous attempts were made to formulate its structure but with difficulty. It is now known that structurally, benzene is the simplest compound typifying aromatic character. Your appreciation of 'aromatic character' will develop with your experience in organic chemistry.<P><B>Here is a brief outline of the evidence leading to the structure of Benzene:</B><OL><LI>Benzene does not readily undergo addition reactions (similar to those of alkenes).<BR><BR><LI>Benzene has no isomers.<DIV ALIGN=center><TABLE BORDER=0><TR><TD WIDTH=275 ALIGN=center>CH<SUB>3</SUB>-C<FONT FACE=Symbol>&#0186;</FONT>C-C<FONT FACE=Symbol>&#0186;</FONT>C-CH<SUB>3</SUB><TD WIDTH=275 ALIGN=center>CH<SUB>2</SUB>=CH-C<FONT FACE=Symbol>&#0186;</FONT>C-CH=CH<SUB>2</SUB><TD WIDTH=275 ALIGN=center>H-C<FONT FACE=Symbol>&#0186;</FONT>C-CH<SUB>2</SUB>-CH<SUB>2</SUB>-C<FONT FACE=Symbol>&#0186;</FONT>C-H</TABLE><BR></DIV><LI>Benzene has no isomers of its monosubstituted derivatives, C<SUB>6</SUB>H<SUB>5</SUB>Y.<P>This suggests a ring structure, proposed by Kekul&#0233; in 1865.<BR><P><CENTER><IMG SRC=benzene1.gif WIDTH=300 HEIGHT=139></CENTER><P><LI>Benzene has three structural isomers of its disubstituted derivative, C<SUB>6</SUB>H<SUB>4</SUB>Y<SUB>2</SUB>.<P>It was pointed out that if one of the above structures were correct then benzene would have four (not three) disubstituted derivatives.<P><CENTER><IMG SRC=benzene2.gif WIDTH=425 HEIGHT=132></CENTER><P>Kekulé then modified his idea proposing that benzene rapidly alternated between the two structures below.<P><CENTER><IMG SRC=benzene3.gif WIDTH=250 HEIGHT=74></CENTER><P>That is, structures I and IV would be in dynamic equilibrium and therefore not separable. But, even this reasoning failed to account for the lack of ease with which benzene undergoes addition reactions.<BR><BR><LI>Resonance Theory (c. 1945). This recognises that one simple structural diagram cannot always adequately represent the distribution of electrons within a molecule. Instead it is necessary to characterise the molecule by various alternative structures, with the true structure lying somewhere between the extremes. Often the structure shown below is used to represent the benzene molecule.<P><CENTER><IMG SRC=benzene.gif WIDTH=75 HEIGHT=75></CENTER><P>Refer to the Resonance page on this web site or to an organic chemistry textbook to read more about resonance theory.</OL>"
}

function cAromatic(){
content.innerHTML="<P><CENTER><IMG SRC=aromatics.gif WIDTH=410 HEIGHT=910></CENTER>"
}