<P> Organic molecules are described more commonly by drawings or structural formulas, combinations of drawings and chemical symbols . The line - angle formula is simple and unambiguous . In this system, the endpoints and intersections of each line represent one carbon, and hydrogen atoms can either be notated explicitly or assumed to be present as implied by tetravalent carbon . </P> <P> By 1880 an explosion in the number of chemical compounds being discovered occurred assisted by new synthetic and analytical techniques . Grignard described the situation as "chaos le plus complet" as due to the lack of convention it was possible to have multiple names for the same compound . This led to the creation of the Geneva rules in 1892 . </P> <P> The concept of functional groups is central in organic chemistry, both as a means to classify structures and for predicting properties . A functional group is a molecular module, and the reactivity of that functional group is assumed, within limits, to be the same in a variety of molecules . Functional groups can have decisive influence on the chemical and physical properties of organic compounds . Molecules are classified on the basis of their functional groups . Alcohols, for example, all have the subunit C-O-H . All alcohols tend to be somewhat hydrophilic, usually form esters, and usually can be converted to the corresponding halides . Most functional groups feature heteroatoms (atoms other than C and H). Organic compounds are classified according to functional groups, alcohols, carboxylic acids, amines, etc . </P> <P> The aliphatic hydrocarbons are subdivided into three groups of homologous series according to their state of saturation: </P>

What determines the properties of organic compounds (points 3)