Locant

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... 

Both remaining CgHi4 isomers have two methyl groups as substituents on a four carbon chain Thus the parent chain is butane When the same substituent appears more than once use the multiplying prefixes di tri tetra and so on A separate locant is used for each substituent and the locants are separated from each other by commas and from the words by hyphens... 

When deciding on the proper direction a point of difference occurs when one order gives a lower locant than another Thus although 2 is the first locant m both numbering schemes the tie is broken at the second locant and the rule favors 2 2 6 6 7 which has... 

Finally when equal locants are generated from two different numbering directions choose the direction that gives the lower number to the substituent that appears first m the name (Remember substituents are listed alphabetically)... 

Number the chain in the direction that gives the lower locant to a substituent at the first point of difference... 

When numbering from left to right the substituents appear at carbons 3 3 and 4 When numbering from right to left the locants are 3 4 and 4 therefore number from left to right... 

Name the alkyl group and append it as a prefix to the cycloalkane No locant is needed if the com pound IS a monosubstituted cycloalkane It is understood that the alkyl group is attached to C 1... 

The longest continuous chain that includes the double bond forms the base name of the alkene and the chain is numbered in the direction that gives the doubly bonded carbons their lower numbers The locant (or numerical position) of only one of the dou bly bonded carbons is specified in the name it is understood that the other doubly bonded carbon must follow in sequence... 

No locants are needed m the absence of substituents it is understood that the double bond connects C 1 and C 2 Substituted cycloalkenes are numbered beginning with the double bond proceeding through it and continuing m sequence around the ring The direction is chosen so as to give the lower of two possible numbers to the substituent... 

The o m and p prefixes are not used when three or more substituents are present on benzene numerical locants must be used instead... 

Using numerical locants and the names in Table 11 1 as a guide give an acceptable lUPAC name for each of the following compounds... 

Diols are almost always given substitutive lUPAC names As the name of the prod uct m the example indicates the substitutive nomenclature of diols is similar to that of alcohols The suffix dwl replaces ol and two locants one for each hydroxyl group are required Note that the final e of the parent alkane name is retained when the suffix begins with a consonant ( diol) but dropped when the suffix begins with a vowel ( ol)... 

Notice that because they define the ends of the carbon chain in 2 phenylbutanedial the aldehyde positions are not designated by numerical locants in the name... 

Section 17 1 The substitutive lUPAC names of aldehydes and ketones are developed by identifying the longest continuous chain that contains the carbonyl group and replacing the final e of the corresponding alkane by al for aldehydes and one for ketones The chain is numbered m the direction that gives the lowest locant to the carbon of the carbonyl group... 

This IS called direct addition ox 1 2 addition (The 1 and 2 do not refer to lUPAC locants but are used m a manner analogous to that employed m Section 10 10 to distin guish between direct and conjugate addition to conjugated dienes)... 

The systematic lUPAC name of ethyl acetoacetate is ethyl 3 oxobutanoate The presence of a ketone carbonyl group is indicated by the designation oxo along with the appro priate locant Thus there are four carbon atoms m the acyl group of ethyl 3 oxobutanoate C 3 being the carbonyl carbon of the ketone function... 

Secondary and tertiary amines are named as N substituted derivatives of primary amines The parent primary amine is taken to be the one with the longest carbon chain The prefix N is added as a locant to identify substituents on the ammo nitrogen as needed... 

Alkylamines are named m two ways One method adds the ending amine to the name of the alkyl group The other applies the principles of sub stitutive nomenclature by replacing the e ending of an alkane name by amine and uses appropriate locants to identify the position of the ammo group Arylammes are named as derivatives of aniline... 

The numbering scheme used for nucleosides maintains the independence of the two structural units The pyrimidine or purine is numbered m the usual way So is the car bohydrate except that a prime symbol ( ) follows each locant Thus adenosine is a nude oside of D nbose and 2 deoxyadenosine is a nucleoside of 2 deoxy d ribose... 

Locant (Section 2 12) In lUPAC nomenclature a prefix that designates the atom that is associated with a particular structural unit The locant is most often a number and the structural unit is usually an attached substituent as in... 

For branching compounds, the parent structure is the longest continuous chain present in the compound. Consider the compound to have been derived from this structure by replacement of hydrogen by various alkyl groups. Arabic number prefixes indicate the carbon to which the alkyl group is attached. Start numbering at whichever end of the parent structure that results in the lowest-numbered locants. The arable prefixes are listed in numerical sequence, separated from each other by commas and from the remainder of the name by a hyphen. 

If the same alkyl group occurs more than once as a side chain, this is indicated by the prefixes di-, tri-, tetra-, etc. Side chains are cited in alphabetical order (before insertion of any multiplying prefix). The name of a complex radical (side chain) is considered to begin with the first letter of its complete name. Where names of complex radicals are composed of identical words, priority for citation is given to that radical which contains the lowest-numbered locant at the first cited point of difference in the radical. If two or more side chains are in equivalent positions, the one to be assigned the lowest-numbered locant is that cited first in the name. The complete expression for the side chain may be enclosed in parentheses for clarity or the carbon atoms in side chains may be indicated by primed locants. 

Eor multiple unsaturated bonds, the chain is so numbered as to give the lowest possible locants to the unsaturated bonds. When there is a choice in numbering, the double bonds are given the lowest locants, and the alkene is cited before the alkyne where both occur in the name. Examples ... 

Univalent radicals have the endings -enyl, -ynyl, -dienyl, -diynyl, etc. When necessary, the positions of the double and triple bonds are indicated by locants, with the carbon atom with the free valence numbered as 1. Examples ... 

The position of substituents is indicated by numbers, with the lowest locant possible given to substituents. When a name is based on a recognized trivial name, priority for lowest-numbered locants is given to substituents implied by the bivial name. When only two substituents are present on a benzene ring, their position may be indicated by o- ortho-), m- meta-), and p- (para-) (and alphabetized in the order given) used in place of 1,2-, 1,3-, and 1,4-, respectively. 

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... 

The lowest-numbered locant for substituents named as prefixes, hydro prefixes, -ene, and -yne, all considered together in one series in ascending numerical order... 

The lowest locant for that substituent named as prefix which is cited first in the name... 

When a cyclic component carries more than one identical side chain, the name of the cyclic component is followed by di-, tri-, etc., and then by the name of the acyclic component, and it is preceded by the locants for the side chains. Examples are... 

When side chains of two or more different kinds are attached to a cyclic component, only the senior side chain is named by the conjunctive method. The remaining side chains are named as prefixes. Likewise, when there is a choice of cyclic component, the senior is chosen. Benzene derivatives may be named by the conjunctive method only when two or more identical side chains are present. Trivial names for oxo carboxylic acids may be used for the acyclic component. If the cyclic and acyclic components are joined by a double bond, the locants of this bond are placed as superscripts to a Greek capital delta that is inserted between the two names. The locant for the cyclic component precedes that for the acyclic component, e.g., indene-A - -acetic acid. 

When the parent molecules connected by the azo group are different, azo is placed between the complete names of the parent molecules, substituted or unsubstituted. Locants are placed between the affix azo and the names of the molecules to which each refers. Preference is given to the more complex parent molecule for citation as the first component, e.g., 2-aminonaphthalene-l-azo-(4 -chloro-2 -methy Ibenzene). 

Many trivial names exist for acids these are listed in Table 1.11. Generally, radicals are formed by replacing -ic acid by -oyL When a trivial name is given to an acyclic monoacid or diacid, the numeral 1 is always given as locant to the carbon atom of a carboxyl group in the acid or to the carbon atom with a free valence in the radical RCO—. 

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