nomenclature - Chemistry 121 Winter 2001 Course Notes...

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Chemistry 121 Winter 2001 Course Notes Principles of Chemistry II Page 7 ORGANIC NOMENCLATURE Introduction Confusion can arise in organic chemistry because of the variety of names that have been applied to compounds; common names, trade names and systematic names are prevalent. For example, a compound of formula, C 6 H 6 O has variously been known as phenol, carbolic acid, phenic acid, phenyl hydroxide, hydroxybenzene, phenylic acid and oxobenzene! To help eliminate the proliferation of many names for a compound, a systematic IUPAC naming system has been derived to uniquely name the several million organic different compounds based on considerations of their structure. This hand-out will address the naming of simple organic compounds and is by no means complete, for instance the compound, hexahydroazepinium-1-spiro-1'-imidazolidine-3'-spiro-1''-piperidinium dibromide may be regarded as being too complicated for this course! In general compounds are classified and named by consideration of: a) the number and types of atoms that are present, b) the bond types in the molecule, and c) the geometry of the molecule. Formulae Prior to setting out the rules for naming compounds it is pertinent to review some aspects of formulae. The molecular formula of a compound gives no explicit information about the structure of the compound. The formula C 2 H 6 O makes no mention as to how the various atoms are arranged, indeed two different compounds share this formula but have different structures and vastly different properties. COH H H C H H H C H H H OC H H H ethanol dimethyl ether By writing their formulae in a structural form we can differentiate between these two compounds. CH 3 2 OH CH 3 CH 2 OH C 2 H 5 OH CH 3 OCH 3 3 H 3 ethanol dimethyl ether or or or In writing these formulae the atoms after a carbon indicate the elements or groups, attached to that carbon. It must be remembered that all C atoms in organic compounds must be involved in four bonds. CH 3 CHClCCl 3 CH 3 CH(CH 3 )CH 2 CH=CH 2 C H H H C H Cl C C H 3 C 3 H C H H C H C H H
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Chemistry 121 Winter 2001 Course Notes Principles of Chemistry II Page 8 C 6 H 5 CH(NH 2 )COOH C H NH 2 C OH O Note: C 6 H 5 invariably refers to a benzene ring (minus a hydrogen atom). COOH or CO 2 H invariably refers to an acid group C O In these examples the bond angles in many instances are drawn as right angles and the molecules appear planar. It should be emphasized that we are drawing 2-dimensional representations of 3-dimensional molecules and that the actual bond angles are rarely of 90 degrees. Configurational structures are sometimes used if the absolute geometry is of importance. propane: C 3 H 8 or CH 3 CH 2 CH 3 or C H H H C H H C H H H or H C C C H H H H H HH where dashed lines represent bonds behind the plane of the page and solid lines are are bonds coming out from the page. All other lines are in the plane of the page and all bond angles are 109 ° .
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nomenclature - Chemistry 121 Winter 2001 Course Notes...

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