Substituent groups

Lines 4—18 form the connection table (Ctah), containing the description of the collection of atoms constituting the given compound, which can be wholly or partially connected by bonds. Such a collection can represent molecules, molecular fragments, substructures, substituent groups, and so on. In case of a Molfile, the Ctah block describes a single molecule. 

A halogen atom directly attached to a benzene ring is usually unreactive, unless it is activated by the nature and position of certain other substituent groups. It has been show n by Ullmann, however, that halogen atoms normally of low reactivity will condense with aromatic amines in the presence of an alkali carbonate (to absorb the hydrogen halide formed) and a trace of copper powder or oxide to act as a catalyst. This reaction, known as the Ullmant Condensation, is frequently used to prepare substituted diphenylamines it is exemplified... 

It must be emphasised that the following substances are merely representative of widely different classes of compounds, and that the test when applied to an unknown compound often provides only a general indication of the probable class to which the compound belongs. Moreoi er, the behaviour of a compound when heated is often determined more by the nature of its substituent groups than by its general character. 

I The phenol cannot always be isolated in good yield, particularly if it contains substituent groups, owing to the destructive action of the alkali fusion upon the radical R. 

The quatemization of 16 2,4-dialkylthiazoles with methyl tosylate in nitrobenzene at 25 C has been studied (256) in order to examine the simultaneous influence of two substituents grouped around a reaction center (257). 

Identify the substituent groups attached to the parent chain... 

Number the longest continuous chain m the direction that gives the lowest number to the substituent group at the first point of branching The numbering scheme... 

Write the name of the compound The parent alkane is the last part of the name and is preceded by the names of the substituent groups and their numerical locations (locants) Hyphens separate the locants from the words... 

As you can see cycloalkanes are named under the lUPAC system by adding the prefix cyclo to the name of the unbranched alkane with the same number of carbons as the ring Substituent groups are identified m fhe usual way Their posifions are specified by numbering fhe carbon atoms of fhe ring m fhe direction fhaf gives fhe lowesf num ber to fhe subsfifuenfs af fhe firsf pomf of difference... 

The substituent groups on the double bonds of most alkenes are of course more com plicated than m this example The rules for ranking substituents especially alkyl groups are described m Table 5 1... 

Radicals from Ring Systems. Univalent substituent groups derived from polycyclic hydrocarbons are named by changing the final e of the hydrocarbon name to -yl. The carbon atoms having free valences are given locants as low as possible consistent with the fixed numbering of the... 

When the compound can be considered as derived from a base whose name does not end in -amine, its quaternary nature is denoted by adding ium to the name of that base (with elision of e), substituent groups are cited as prefixes, and the name of the anion is added separately at the end. Examples are... 

When the asymmetric carbon atoms in a chiral compound are part of a ring, the isomerism is more complex than in acyclic compounds. A cyclic compound which has two different asymmetric carbons with different sets of substituent groups attached has a total of 2 = 4 optical isomers an enantiometric pair of cis isomers and an enantiometric pair of trans isomers. However, when the two asymmetric centers have the same set of substituent groups attached, the cis isomer is a meso compound and only the trans isomer is chiral. (See Fig. 1.15.)... 

Table 7.51 Effect of Substituent Groups on Alkyl Chemical Shifts 7.102...

Sets of empirical rules, often referred to as Woodward s rules or the Woodward-Fieser rules, enable the absorption maxima of dienes (Table 7.11) and enones and dienones (Table 7.12) to be predicted. To the respective base values (absorption wavelength of parent compound) are added the increments for the structural features or substituent groups present. When necessary, a solvent correction is also applied (Table 7.13). 

Substituent group Methyl protons Methylene protons Methine proton... 

Substituent group shift Substituent group shift... 

Positive Z values indicate a downfield shift, and an arrow indicates the point of attachment of the substituent group to the double bond. 

Substituent group Primary carbon Secondary carbon Tertiary carbon Quaternary carbon... 

Substituents on both sides of the double bond are considered separately. Additional vinyl carbons are treated as if they were alkyl carbons. The method is applicable to alicyclic alkenes in small rings carbons are counted twice, i.e., from both sides of the double bond where applicable. The constant in the equation is the chemical shift for ethylene. The effect of other substituent groups is tabulated below. 

The product molecules usually have a carbon chain backbone, with pendant substituent groups... 

For most vinyl polymers, head-to-tail addition is the dominant mode of addition. Variations from this generalization become more common for polymerizations which are carried out at higher temperatures. Head-to-head addition is also somewhat more abundant in the case of halogenated monomers such as vinyl chloride. The preponderance of head-to-tail additions is understood to arise from a combination of resonance and steric effects. In many cases the ionic or free-radical reaction center occurs at the substituted carbon due to the possibility of resonance stabilization or electron delocalization through the substituent group. Head-to-tail attachment is also sterically favored, since the substituent groups on successive repeat units are separated by a methylene... 

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