Organichemica
Basic Organic Chemistry

A Tutorial

Dave Woodcock ©2001

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Glossary

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Glossary Index


carbanion

An organic anion in which the electron excess resides (at least partially) on a carbon atom.

carbene

An organic species containing a divalent carbon (two bonds). The species also contains two unbonded electrons and is highly reactive and an electrophile, having only 6 electrons round carbon instead of the usual 8: it must be prepared and used immediately.
singlet carbene: in this species the two electrons are paired in an sp2 orbital and an 'empty' p orbital is present. In a reaction the electrons react as a pair.
triplet carbene: in this species the two electrons are present one in each of the sp2 and p orbitals and the electrons are unpaired, it is a diradical. In a reaction the electrons can react individually with the formation of an intermediate diradical species.

carbocation

An organic species containing a tervalent positively charged carbon with 6 electrons. The geometry of the species is trigonal planar at the positive carbon with the electron deficiency in an 'empty' p orbital. Lacking the octet, the species is a highly reactive electrophile proposed as an intermediate in reactions rather than an isolable compound.

Electron donating groups will stabilize the cation, as will interaction with sigma bonds on adjacent atoms. This carbon substituted carbocations are stabilized in the order:
1o less than 2o less than 3o.

carbon radical

An organic species containing a tervalent carbon with 7 electrons. The geometry of the species is tetrahedral (though the methyl radical is trigonal planar) at the tervalent carbon with the electron deficiency as a single electron in an sp3 orbital. Lacking the octet, the species is a highly reactive electrophile proposed as an intermediate in reactions rather than an isolable compound.

Electron donating groups will stabilize the radical, as will interaction with sigma bonds on adjacent atoms. This carbon substituted radicals are stabilized in the order:
1o less than 2o less than 3o.

catalyst

A species which increases the rate of a chemical process without being used up by it.
The catalyst is involved in the reaction, being used in one step and regenerated in a later step. This involvement produces a new stepwise process which has a lower activation energy than the process without the catalyst, and which is therefore faster.

cation

A positively charged atom or group of atoms. If the postive charge is due to an electron deficient carbon atom, the term carbocation is used.

chain reaction

Chain reactions are typically radical reactions because radicals have an odd electron which must be preserved when reacting with an even electron species. Radical chain reactions can be divided into three distinct processes:

1. Initiation steps, in which a radical is formed.

2. Chain steps, in which a radical reacting with a neutral (even electron) species forms a new radical which can continue the reaction.
Often, a radical reacting in one step is reformed in a subsequent step.

These steps are usually repeated many times before feature 3 occurs.

3. Termination steps, in which radicals are distroyed (two radicals react with each other) thereby stopping the chain.

chiral

A molecule with a non-superposable mirror image is said to be chiral.
Chirality is a property of the whole molecule rather than a part of it.
The two mirror images are termed enantiomers (there are only ever two enantiomers of a particular structure!)

chirality centre

An atom in a molecule which is unsymmetrically substituted such that exchanging two attached groups (atoms) with each other will result in a new isomer which is a stereoisomer of the first molecule.
A carbon atom attached to four different groups (atoms) is a chirality centre.
When only one chirality centre is present in a molecule, the molecule itself is chiral, existing as two stereoisomers which are mirror images of each other. Stereoisomers which are mirror images of each other are termed enantiomers.
A number of older names for this centre occur, such as stereogenic centre, chiral centre, and asymmetric centre.

conditions

The conditions of a reaction usually indicate the solvent, temperature and duration for a reaction. They are ofter listed over (and/or under) the reaction arrow.

covalent bonding

An atom to atom bond involving the sharing of electrons between the two atoms.

curved or curly arrows

A curved arrow indicating the flow of electrons during a reaction step. The electron flow follows the direction of the arrow. The tail of the arrow indicates where the electrons are at the start of the reaction or step, the head indicates where they will be at the end of the reaction (step).
A full-headed arrow indicates the movement of two electrons.
A half-headed arrow indicates the movement of one electron.

Glossary Index
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N O P Q R S T U V W X Y Z

Main Index

page upkeep: Dave.
I would appreciate comments and additions by email to:
woodcock@okanagan.bc.ca
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