Group formation

Stretching then breaking of the bond to the leaving group Formation of a bond to the nucleophile from the opposite side of the bond that is broken... 

Many reagents are able to chlorinate aromatic pyrazole derivatives chlorine-water, chlorine in carbon tetrachloride, hypochlorous acid, chlorine in acetic acid (one of the best experimental procedures), hydrochloric acid and hydrogen peroxide in acetic acid, sulfuryl chloride (another useful procedure), etc. iV-Unsubstituted pyrazoles are often used as silver salts. When methyl groups are present they are sometimes chlorinated yielding CCI3 groups. Formation of dimers and trimers (308 R = C1) has also been observed. 

Substitution of the hetero group (XR ) at C-1 by the amino group (intermediate 149) and cyclization of its tautomer (150) with the participation of the methylene group (formation of 2,4-isomer 147). 

Step 1 of Figure 27.7 Claisen Condensation The first step in mevalonate biosynthesis is a Claisen condensation (Section 23.7) to yield acetoacetyl CoA, a reaction catalyzed by acetoacetyl-CoA acetyltransferase. An acetyl group is first bound to the enzyme by a nucleophilic acyl substitution reaction with a cysteine —SH group. Formation of an enolate ion from a second molecule of acetyl CoA, followed by Claisen condensation, then yields the product. 

Establishment of the detailed microstructure of PVC has attracted considerable interest. This has been spurred by the desire to rationalize the poor thermal stability of the polymer (Chapter 1). Many reviews have appeared on the chemical microstruclure of PVC and the mechanisms of defect group formation.56 60... 

In Reaction 12-9 treatment of Z—CH2—Z with tosyl azide gives diazo transfer. When this reaction is performed on a compound with a single Z group, formation of the azide becomes a competing process. " Factors favoring azide formation rather than diazo transfer include as the enolate counterion rather than Na orLi and... 

The Pectolyase Y-23 catalytic activity was studied on several solutions of pectin at pH 3.0 and 6.0 and of polygalacturonic acid at pH 4.1. During pectin depolymerisation, the PL activity is about 20 times lower than the one of the PG and reaches its saturation value after about 30 min whereas the PG activity increases regularly with time. This dual behaviour is probably connected to the competitive hydrolytic action of PE that quickly transforms the pectin into the polygalacturonic acid. Accordingly, the reducing group formation is mainly due to the PG action and the pectin depolymerisation derives from the sequential action of PE and PG. 

Figure 2. Kinetic curve of POOH groups formation in polypropylene film after 10 hours exposure to ozone.

ATR spectra show that oxygen groups are located at the surface to the depth of 0.6 /l m. Kinetic curves of carbonyl groups formation in different experimental conditions are shown in Fig.4. 

Figure 4. Kinetics of carbonyl group formation at 1714 cm- in polypropylene samples (0) and ( ) ozone and UV light (L2) (4) and (A) ozone only (0) and ( ) ATR spectra (A) and (A) transmission spectra.

Extrapolating from prior examples of group formation to future possibilities is a deductive process, and so it is perhaps not so unusual to bring Arthur Conan Doyle s Sherlock Holmes into the discussion. As devoted readers will testify, Conan Doyle s stories are filled with physical details, particularly those relating to the persons and behaviors of his characters. Some of those physical traits are immediately observable to other characters in the stories, whereas other physical traits are apparent only after their logical relation to human actions are made evident by Holmes. 

FIGURE 8.21 Proposed mechanism for the BOP-Cl-mediated reaction of a carboxylate anion with a methylamino group. Formation of a mixed anhydride is followed by aminolysis that is facilitated by anchimeric assistance provided by the oxygen atom of the ring carbonyl.101 (van der Auwera Anteunis, 1987). BOP-C1 = fcw(2-oxo-3-oxazolidino)phosphinic chloride. 

J Data presented as equilibrium constant K, rate constant (m3 mol-1 min-1) and activation energy Ea (kJmol-1). Reaction orders 2, for esterification, polycondensation and polycondensation of tV 3, for H+ catalyzed reactions 1, for diester group formation and AA degradation. b irrev, irreversible. 

Photolytic. Photoproducts reported from the sunlight irradiation of propanil (200 mg/L) in distilled water were 3 -hydroxy-4 -chloropropionanilide, 3 -chloro-4 -hydroxypropionanilide, 3, 4 -di-hydroxypropionanilide, 3 -chloropropionanilide, 4 -chloropropionanilide, propionanilide, 3,4-di-chloroaniline, 3-chloroaniline, propionic acid, propionamide, 3,3, 4,4 -tetrachloroazobenzene, and a dark polymeric humic substance. These products formed by the reductive dechlorination, replacement of chlorine substituents by hydroxyl groups, formation of propionamide, hydrolysis... 

---