Functional Group Classification E& G-Functions. From the preceding discussion, one might (..)(/E-function the creation of four classes of functional groups, however, for the sake o simplicity, three FG class designations will be chosen. To organize activating (+)((+ functions into common categories it is worthwhile to define " hypothetical functional groups E, and G, I having the charge affinity patterns denoted in 6 nd 7 respectively. Given the appropriate oxidation state of the carbon skeleton such functional groups confer the indicated potential site reactivity patterns Hypothetical G-function towards both electrophilic and nucleophilic reagents. Any functional groups ((+)6 whose reactivity pattern conforms to the ideal pattern or to a sub-pattern of C-C-C-G these hypothetical functions will be thus classified as an E- or G-function respectively. For example, the halogen and oxygen-based functional groups in four molecules illustrated in Scheme Ill may be classified as E-functions since their respective charge affinity patterns conform to a subset of the charge affinity pattern of the hypothetical E-function A-Functions. A third hypothetical function, A, (A for amphoteric!) can be defined which has an unbiased charge Hypothetical A-function affinity pattern as in 8. Such an idealized functional group (+-( activates all sites to both nucleophilic and electrophilic reactions and. as such. include those functions classified as either e or g The importance of introducing this third class designation is that it includes those functional groups having non-al ternate charge affinity patterns as in 9, 10 and 11 The differentiation of polar reactivity patterns can be described in an alternative manner. Starting with an ideal A-function, one could imagine a process in which the reactivity pattern is gradually polarized towards E-or G-behavior(Scheme V). Since site reactivity is not an on-off property but varies continu- usly over a wide range, one could further subdivide a-class functions into those functions with a bias towards E-class or G-class properties. Such a bias could be denoted by the dominant subordinate charge affinity notation in 12 and 13; however, for the concepts to be presented in this discourse, such A-function subclasses are nonessential. It should be emphasized that the purpose of the E-and G-classification is not to rigidly pigeon-hole functional groups based on site reactivity, but only to separate those which are strongly polarized toward e or g behavior. The decision has been made to avoid the pursuit of an overly detailed FG classification scheme since such attempts will dangerously oversimplify problems since an es sentially contiguous function cannot be segmented in to discrete part Scheme V Alternate vs Nonalternate Reactivity Patterns Hypothetical A-function (+-)(+-)(+-) 8(_A Hypothetical E-function Hypothetical G-function I) The symbol E was selected to denote electrophilic at the point of attachment to the carbon skeleton Unfortunately,the symbol N cannot be used to represent those FGs which are nucleophilic at the point of attachment since this is also the symbol for nitrogen. To avoid this conflict, the symbol g was chosen for this FG class designationFunctional Group Classification page 4 E & G-Functions. From the preceding discussion, one might opt for the creation of four classes of functional groups; however, for the sake of simplicity, three FG class designations will be chosen. To organize activating functions into common categories it is worthwhile to define "hypothetical" functional groups E, and G,11 having the charge affinity patterns denoted in 6 and 7 respectively. Given the appropriate oxidation state of the carbon skeleton, such functional groups confer the indicated potential site reactivity patterns towards both electrophilic and nucleophilic reagents. Any functional groups whose reactivity pattern conforms to the ideal pattern or to a sub-pattern of these hypothetical functions will be thus classified as an E- or G-function respectively. For example, the halogen and oxygen-based functional groups in four molecules illustrated in Scheme III may be classified as E-functions since their respective charge affinity patterns conform to a subset of the charge affinity pattern of the hypothetical E-function. A-Functions. A third hypothetical function, A, (A for amphoteric!) can be defined which has an unbiased charge affinity pattern as in 8. Such an idealized functional group activates all sites to both nucleophilic and electrophilic reactions and, as such, include those functions classified as either E or G. The importance of introducing this third class designation is that it includes those functional groups having non-alternate charge affinity patterns as in 9, 10 and 11. The differentiation of polar reactivity patterns can be described in an alternative manner. Starting with an ideal A-function, one could imagine a process in which the reactivity pattern is gradually polarized towards E- or G-behavior (Scheme V). Since site reactivity is not an on-off property but varies continu￾ously over a wide range, one could further subdivide A-class functions into those functions with a bias towards E-class or G-class properties. Such a bias could be denoted by the dominant subordinate charge affinity notation in 12 and 13; however, for the concepts to be presented in this discourse, such A-function subclasses are nonessential. It should be emphasized that the purpose of the E- and G-classification is not to rigidly pigeon-hole functional groups based on site reactivity, but only to separate those which are strongly polarized toward E or G behavior. The decision has been made to avoid the pursuit of an overly detailed FG classification scheme since such attempts will dangerously oversimplify problems since an es￾sentially contiguous function cannot be segmented in to discrete parts. C C C A C C C A C C C A C C C G C C C E (+–) (+–) (+–) 12 Hypothetical A-function (±) (±) (±) (±) (±) (±) (–) (+) (–) (+) (–) (+) Hypothetical E-function Hypothetical G-function Scheme V Alternate vs Nonalternate Reactivity Patterns 13 11) The symbol E was selected to denote electrophilic at the point of attachment to the carbon skeleton Unfortunately, the symbol N cannot be used to represent those FGs which are nucleophilic at the point of attachment since this is also the symbol for nitrogen. To avoid this conflict, the symbol G was chosen for this FG class designation. C C C E C C C G (+) (–) (+) 6 7 (–) (+) (–) Hypothetical E-function Hypothetical G-function C C C A C C A C C A C A Hypothetical A-function 8 (+–) (+–) (+–) 9 (+) (+) (–) (–) 10 11 (+–)