Roberts, Caserio - Basic Principles of Organic Chemistry (2nd edition, 1977)

7-70 Amides, RCONH,

II

7-7D Amides, RCNH,

1. The suffix amide is appended to the name of the hydrocarbon corresponding to the carbon chain that includes the carbonyl group. That is, alkan(e) +amide = alkanamide. A one-carbon chain is a carboxamide:

2. When the amide nitrogen is substituted with lower-ranking groups than the acyl group, the substituents are designated as prefixes. The letter N is used to show that the substitution is on nitrogen:

7 C-N, 7".

3. Names for amides as substituents include the following:

I

ethyl 3-(4-N-methylcarbamoylcyclohexyl)propanoate

Exercise 7-9 Give the systematic names for each of the following compounds:

2. Secondary and tertiary amines, which have two and three substituents on nitrogen, commonly are named as N-substituted amines. As for substituted amides, N is included to indicate that the substituent is on the nitrogen atom unless there is no ambiguity as to where the substituent is located. Systematic nomenclature of secondary and tertiary amines is related to the systematic ether nomenclature discussed in Section 7-3:

3. As a substituent, the -NH2 group is called amino. N-Substituted amino groups are named accordingly:

Exercise 7-11 Determ~nethe systernat~cnames for the following compounds

IAlphabetical order puts chloro- ahead of chloroethyl-.

7-9 NITRILES, RCN

1. Compounds with the =N function are named by adding the suffix nitvile to the main-chain hydrocarbon that includes the carbon linked to the nitrile (=N) function. The chain is numbered so the CN carbon is C1:

2. Compounds of the type RCN have to be called cavbonitriles when R is a cycloalkane or similar group:

CN

cyclohexanecarbonitrile 1,4-benzenedicarbonitrile

3. Nitriles can be regarded as derivatives of carboxylic acids because the acid, RCO,H, usually can be obtained from the nitrile, RCN:

A common system of naming nitriles takes the name of the corresponding carboxylic acid and changes the suffix -oic to -onitvile:

Exercise 7-12 Determine the systematic names for each of the following compounds:

7-10 THE USE OF GREEK LETTERS TO DENOTE SUBSTITUENT POSITIONS

In the older literature, considerable use is made of the Greek letters a, P, y , and so on, to designate successive positions along a hydrocarbon chain. The carbon directly attached to the principal functional group is denoted as a, the second carbon is p, and so on down the chain:

c,. . . . . . . C~-C,-CB-C,-X

t

functional group

The omega (a) position sometimes is used to designate the last position along the chain regardless of its length. Thus a-bromohexanoic acid is 6-bromo- hexanoic acid. In general, the use of Greek letters in the naming of compounds is to be avoided. Because the usage is widespread, cognizance of the system is important, but systematic naming and numbering systems should be used whenever possible.

7-11 SINGLEOR MULTIPLE-WORD NAMES

A troublesome point in naming chemical compounds concerns the rules governing when a compound is to be written as a single word (as methylamine) or as two or more words (as methyl chloride). T o solve this problem, you must determine whether the principal or parent function is an element or a compound in its own right; if it is either one, then the name is written as a single word.

The following examples should help to clarify the system. In each name, the part of the name that denotes the parent compound2 is italicized:

However, if the parent function cannot be construed as being a real compound, the name is correctly written as two or more words. For example, CH,Cl could be named as a chloride, in which case we use two words, methyl chloride, to describe it. A chloride, or any halide, is a class of compound, not a specific compound. To identify a specific halide, the adjective that describes the halide is written as a separate word preceding the class name. Examples follow in which the class name is italici~ed:~

Additional Reading

J. H. Fletcher, 0. C. Dermer, and R. B. Fox, Nomenclature of Organic Compounds. Principles and Practice, Advances in Chemistry Series, 126, American Chemical Society, Washington, D.C., 1974.

2The parent compounds designated here as amine, carbaldehyde, and sulfonic acid are properly ammonia, methanal, and sulfurous acid (HS0,H) when no substituent groups are attached.

,These word-separated names sometimes are called radicofunctional names.

8-1 Classification of Reagents as Electrophiles and Nucleophiles. Acids and Bases

There are a large number of reactions, usually occurring in solution, that do not involve atoms or radicals but rather involve ions. They occur by heterolytic cleavage as opposed to homolytic cleavage of el~ctron-pairbonds. In heterolytic bond cleavage, the electron pair can be considered to go with one or the other of the groups R and X when the bond is broken. As one example, Y is a group such that it has an unshared electron pair and also is a negative ion. A heterolytic substitution reaction in which the R:X bonding pair goes with X would lead to RY and :X?

R ~ : X+ :YO --':x@+ R : Y a heterolytic substitution reaction

A specific substitution reaction of this type is that of chloromethane with hydroxide ion to form methanol:

In this chapter, we shall discuss substitution reactions that proceed by ionic or polar mechanisms' in which the bonds cleave heterolytically. We also will discuss the mechanistically related elimination reactions that result in the formation of carbon-carbon multiple bonds:

/\

These reactions often are influenced profoundly by seemingly minor variations in the structure of the reactants, in the solvent, or in the temperature. It is our purpose to show how these reactions can be understood and how they can be used to prepare other useful organic compounds. But first it will be helpful to introduce the concepts of nucleophilic and electrophilic reagents, and to consider the AH values for heterolytic bond breaking.

8-1 CLASSIFICATION OF REAGENTS AS ELECTROPHILES AND NUCLEOPHILES. ACIDS AND BASES

To understand ionic reactions, we need to be able to recognize whether a particular reagent will act to acquire an electron pair or to donate an electron