Group equivalent reaction

The group equivalent algorithm does not specify a unique reaction, but only a specification that groups be conserved. The last two entries of Table 3.21 demonstrate two different group equivalent reactions that can be used to estimate the RSE... 

Figure 3.5 Comparison of RSE versus ring size for the cyclic ethers evaluated using CRSE, isodesmic, homodesmotic, and group equivalent reactions.

Figure 3.6 Plots of RSE (group equivalent reaction) for the compounds of Table 3.21 determined using experimental heats of formation versus those determined using (a) G2MP2 energies, (b) HF/6-31G(d) energies, or (c) B3LYP/6-31+G(d) energies.

Bachrach, S. M. The group equivalent reaction an improved method for determining ring strain energy, J. Chem. Ed. 1990,67,907-908. 

Phenol condenses with phthahc anhydride in the presence of concentrated sulphuric acid or anhydrous zinc chloride to yield the colourless phenolphthalein as the main product. When dilute caustic alkah is added to an alcoholic solution of phenolphthalein, an intense red colouration is produced. The alkali opens the lactone ring in phenolphthalein and forms a salt at one phenolic group. The reaction may be represented in steps, with the formation of a h3q)othetical unstable Intermediate that changes to a coloured ion. The colour is probably due to resonance which places the negative charge on either of the two equivalent oxygen atoms. With excess of concentrated caustic alkali, the first red colour disappears this is due to the production of the carbinol and attendant salt formation, rendering resonance impossible. The various reactions may be represented as follows ... 

Fig. 11. Reaction of ionized coupler and oxidized developer (Dev ) to produce the intermediate leuco dye. If X is a good leaving group, the reaction proceeds spontaneously to dye, and the coupler is said to be two-equivalent. If oxidation by a second molecule of oxidized developer is required, the...

Thus, reduction of the Mannich reaction product (65) from acetophenone leads to alcohol 66. Replacement of the hydroxyl group by chlorine (67) followed by displacement of halogen with the anion from o-cresol affords the ether 68. Removal of one of the methyl groups on nitrogen by means of the von Braun reaction or its modem equivalent (reaction with alkyl chloroformate followed by saponification) leads to racemic 69 which is then resolved with L-(+)-mandelic acid to give the levorotary antidepressant tomoxetine (69) [16]. 

The above examples contain an ester group that acts as a second activating group. The reactions are also accelerated by including one equivalent of (CF3)2CHOH. This alcohol functions by promoting solvolysis of a dihydropyran intermediate that otherwise inhibits the catalyst. 

The most versatile synthesis involves the transmetallation of a zirconiacyclopentadiene231,232 with a tin halide under catalysis with CuCl233 (and an equivalent reaction occurs with other halides of other elements of Groups 13, 14, 15, and 16) (Equation (77)). Stannacyclopentenes can be prepared by analogous reactions of zirconacyclopentenes.233... 

Calculated for equimolar exchange with carboxyl groups (NaHCOg and NajCOj neutralization) and equivalent reaction with phenol groups. 

Spectrophotometry has been a popular means of monitoring redox reactions, with increasing use being made of flow, pulse radiolytic and laser photolytic techniques. The majority of redox reactions, even those with involved stoichiometry, have seeond-order characteristics. There is also an important group of reactions in which first-order intramolecular electron transfer is involved. Less straightforward kinetics may arise with redox reactions that involve metal complex or radical intermediates, or multi-electron transfer, as in the reduction of Cr(VI) to Cr(III). Reactants with different equivalences as in the noncomplementary reaction... 

The related geminal dilithiated compound 11 was generated by the same group by reaction of a substituted sulphoximine with 2.5 equivalents of n-butyllithium in THF (Figure 4) Also in this case, the crystal structure of the dilithium compound could be cleared up by X-ray structural analysis (Figure 5). 

The regiochemistry of the reaction of unsymmetrical allylic esters was addressed by the introduction of a silyl group, equivalent to H, on the carbon of the allylic terminus. Eor example, 25 bearing a BuMe2Si group afforded 26 as the sole product in the three-component coupling. Since the subsequent protodesilylation of 26 selectively formed 27 (Scheme 6.6), this sequential procedure provides a practical method to control the regiochemistry in the substitution of unsymmetrical allylic substrates [13 c]. 

The addition of lithioalkanes to d henylvinylarsane according to Schsne 29 constitutes an equivalent reaction, for the diphenylarsanyl group of the resulting primary alkyl-d henyi-araane is readfly replaceable by halc ns whkh are in turn replaceable by lithium in a well-known reaction ... 

Any reaction in Eqs. (1) may be written as a conventional chemical equation by setting it equal to zero and transposing the negative terms to the other side of the equation. This notation has been discussed by Aris (14). Chemical equality, denoted by the symbol has been shown by Sellers (15) to be a group equivalence, thus satisfying ordinary rules of mathematical equality. Except when specific reservations are stated, every reaction is assumed to be reversible, that is, to be capable of any real rate of advancement, positive or negative. 

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