Continuous chain

Proteins are biopolymers formed by one or more continuous chains of covalently linked amino acids. Hydrogen bonds between non-adjacent amino acids stabilize the so-called elements of secondary structure, a-helices and / —sheets. A number of secondary structure elements then assemble to form a compact unit with a specific fold, a so-called domain. Experience has shown that a number of folds seem to be preferred, maybe because they are especially suited to perform biological protein function. A complete protein may consist of one or more domains. 

Methane is the only alkane of molecular formula CH4 ethane the only one that is C2H6 and propane the only one that is C3Hj Beginning with C4H10 however constitutional isomers (Section 1 8) are possible two alkanes have this particular molecular formula In one called n butane, four carbons are joined m a continuous chain The nmn butane stands for normal and means that the carbon chain is unbranched The second isomer has a branched carbon chain and is called isobutane... 

In this case the longest continuous chain has five carbon atoms the compound is named as a derivative of pentane The key word here is continuous It does not matter whether the carbon skeleton is drawn m an extended straight chain form or m one with many bends and turns All that matters is the number of carbons linked together m an uninterrupted sequence... 

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... 

Both schemes count five carbon atoms m their longest continuous chain and bear a methyl group as a substituent at the second carbon An alternative numbering sequence that begins at the other end of the chain is incorrect... 

Branched alkyl groups are named by using the longest continuous chain that begins at the point of attachment as the base name Thus the systematic names of the two C3H7 alkyl groups are propyl and 1 methylethyl Both are better known by their common names n propyl and isopropyl respectively... 

As numbered on the structural formula the longest continuous chain contains eight car bons and so the compound is named as a derivative of octane Numbering begins at the end nearest the branch and so the ethyl substituent is located at C 4 and the name of the alkane is 4 ethyloctane... 

Find the longest continuous chain of carbon atoms and assign a basis name to the compound corresponding to the lUPAC name of the unbranched alkane having the same number of carbons... 

The longest continuous chain in the alkane shown is SIX carbons... 

Number the carbon atoms beginning at the point of attachment proceeding in the direction that follows the longest continuous chain... 

The longest continuous chain that begins at the point of attachment in the group shown contains six carbons... 

The lUPAC rules permit alkyl halides to be named m two different ways called func twnal class nomenclature and substitutive nomenclature In functional class nomencla ture the alkyl group and the halide (fluoride chloride bromide or iodide) are desig nated as separate words The alkyl group is named on the basis of its longest continuous chain beginning at the carbon to which the halogen is attached... 

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... 

The longest continuous chain that contains the —CH group provides the base name for aldehydes The e ending of the corresponding alkane name is replaced by al and sub stituents are specified m the usual way It is not necessary to specify the location of O... 

The longest continuous chain contains three carbons and C 2 is the carbon of the carbonyl group The substitutive lUPAC name for this ketone is 7 3-diphenyl-2- propanone ... 

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... 

Systematic names for carboxylic acids are derived by counting the number of car bons m the longest continuous chain that includes the carboxyl group and replacing the e ending of the corresponding alkane by oic acid The first three acids m Table 19 1 methanoic (1 carbon) ethanoic (2 carbons) and octadecanoic acid (18 carbons) illus trate this point When substituents are present their locations are identified by number... 

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. 

List the substituents attached to the longest continuous chain in alphabetical order. Use the prefixes di-, tri-, tetra-, and so on, when the same substituent appears more than once. Ignore these prefixes when alphabetizing. 

With ketones, the -e ending of an alkane is replaced by -one in the longest continuous chain containing the carbonyl group. The chain is numbered in the direction that provides the lower number for this group. The carbonyl carbon of a cyclic ketone is C-1 and the number does not appear- in the nfflne. 

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