I-strain

It is noteworthy that only in the case of dehydroquinolizidine derivatives does monomethylation produce the N-alkylated product. The formation of dialkylated products can be explained by a disproportionation reaction of the monoalkylated immonium salt caused by either the basicity of the starting enamine or some base added to the reaction mixture (most often potassium carbonate) and subsequent alkylation of the monoalkylated enamine. Reinecke and Kray 113) try to explain the different behavior of zJ -dehydroquinolizidine and zJ -dehydroquinolizidine derivatives by the difference in energies of N- and C-alkylation transition states because of the presence of I strain. 

Fig. 44a. Theoretical molecular weight distribution of a polymer sample degraded along the central streamline at different strain rates, calculated with a pre-exponential factor A = 1014s-1 (I) strain rate e = 75000s-1 (II) strain rate e = 88000s-1 (III) strain rate e = 190000 s- b Theoretical molecular weight distribution of a polymer sample degraded along the central streamline at different strain rates, calculated with A = 104 s-1 (I) strain rate e = 100000 s -1 (II) strain rate e = 120000 s 1 (III) strain rate e = 300000 s -1 (Solid line polymer before degradation, dotted line, degraded polymer)...

Arriving for his first day at the old tobacco warehouse that housed Kettering s firm, Dayton Engineering Laboratories Company, Midgley recalled, I was trying to open the door that looked like the front door of the building, but which was locked. As I strained and pulled at it, a rather lanky individual called out to me, Hey, bud, the architects just stuck that door on to look right to fool people. You get in on the side. Follow me. ... 

Segovia L, Young JP, Martinez-Romero E (1993) Reclassification of American Rhizobium legu-minosarum biovar phaseoli type I strains as Rhizobium etli sp. nov. Int J Syst Bacteriol 43 374-377... 

Changes in I strain bring about changes in the hybridization of the carbon atom during the reaction. Thus in the reduction of the ketones the trigonal sp2 hybridized carbon changes to tetrahedral carbon atom. 

Changes in I-strain may be considered in terms of changes in hybridization from Sp2 to Sp3 or arise vice versa. If the change from Sp2 to Sp3 is accompanied by an increase in I-strain, the reaction would be hindered and those from Sp3 to Sp2 would be facilitated. 

The cations 18a and 19a are predicted to be distorted, the bridge atom (7) being tilted towards the double bond of 18 or one double bond of 19 and the hydrogen atom tilted away this is exactly what would be expected if the ions are it complexes 38) in which one double bond forms a dative bond to the 7-carbon atom. It is perhaps surprising that the saturated cation (18a) shows a similar deformation presumably I-strain at the 7-position favours a 7r-complex-like structure in which a C-C a bond acts as donor. 

TF, Swiss Webster strain from the Tumblebrook Farms. CF, CF1 strain (white) from the Carworth Farms. BF, N.H.I. strain from the Beverly Farms, SD1, Sharp Dohme colony of mice originated from the Webster strain. SD2, another Sharp Dohme strain also originated from the Webster strain. 

It was a dark night. I didn t see the tree in the fog and my uncertainty mounted as the dim streetlights took on the quality of a dream. As I strained to see beyond my fogged windshield, I felt an abrupt jolt as the front of my car went headfirst into a tree. ... 

Many destination vectors are commercially available. However, it is also possible to construct a destination vector that is suitable for individual experiments. To constrnct snch vectors, one should insert the rr ffi-containg cassette (commercially available from Invitrogen) into the appropriate locns of a Gateway-incompatible vector. The resultant plasmids can be amplified only in the DB3.I strain, due to the toxic ccd gene (7). 

The mechanism involving simple nitrogen-coordinated complexes also accounts for reactivities of certain sterically constrained systems. For instance, 3-(diethyamino)cyclohexene undergoes facile isomerization by the action of the BINAP-Rh catalyst (Scheme 18). The atomic arrangement of the substrate is ideal for the mechanism to involve a three-centered transition state for the C—H oxidative addition to produce the cyclometalated intermediate. The high reactivity of this cyclic substrate does not permit any other mechanisms that start from Rh-allylamine chelate complexes in which both the nitrogen and olefinic bond interact with the metallic center. On the other hand, fro/tt-3-(diethylamino)-4-isopropyl-l-methylcyclohexene is inert to the catalysis, because substantial I strain develops during the transition state of the C—H oxidative addition to Rh. 

I-strain,8 and is appreciable when the groups concerned are polar in nature, as for OH, CH2OH, or CHOH—CHjOH. Interactions of such groups at C-l or C-4 with the ring-oxygen atom are considered to be at a minimum. Formula (2) is a pictorial representation of the planar conformation of... 

Figure 9-2. Sinusoidal stain and stress cycles. I strain, amplitude a II in-phase stress, amplitude b III out-of-phase stress, amplitude c IV total stress (resultant of II and III, amplitude d. a is the loss angle...

West (91), amplifying on these results, argued that since the solvolysis is bimolecular it must proceed either through a normal Sn2 bimolecular displacement or involve a rather stable pentacovalent intermediate. Both mechanisms. West believes, must involve a 5-coordinate transition state, and therefore may really be thought of as equivalent. West found that silacyclopentane was 13 times as reactive as diethylmethylsilane and 200 times as reactive as silacydohexane (which could be construed as evidence for I-strain in silacyclopentane). Since this order of reactivity is the same as that found in carbocyclic compounds, it was concluded that similar considerations of energy and entropy of reaction are encountered, a possibility that had also been advanced by Price. 

TABLE i. Strain energies (kcal mol 1) caicuiated using homodesmotic reactions0... 

Since all of the tumors at Cancer Institute are entered in a computer bank (as mentioned in Table I), a descriptive identification system has been adopted (Table II). The computer name of a tumor contains four pieces of information i) strain of origin ii) mode of induction iii) cell type and iv) accession number. 

Kinetics and activation parameters for the oxidation of phenol with tetrakis(pyridine) cobalt(II) chromate have been determined.16 The oxidation of oximes of cyclopen-tanone, cyclohexanone, and cycloheptanone with pyridinium fluorochromate is first order each in the oxidant and oxime. The observed reactivity sequence has been rationalized on the basis of I-strain.17... 

A Cr(VI)-catalyst complex has been proposed as the reactive oxidizing species in the oxidation of frans-stibene with chromic acid, catalysed separately by 1,10-phenanthroline (PHEN), oxalic acid, and picolinic acid (PA). The oxidation process is believed to involve a nucleophilic attack of the olefinic bond on the Cr(VI)-catalyst complex to generate a ternary complex.31 PA- and PHEN-catalysed chromic acid oxidation of primary alcohols also is proposed to proceed through a similar ternary complex. Methanol- reacted nearly six times slower than methanol, supporting a hydride transfer mechanism in this oxidation.32 Kinetics of chromic acid oxidation of dimethyl and diethyl malonates, in the presence and absence of oxalic acid, have been obtained and the activation parameters have been calculated.33 Reactivity in the chromic acid oxidation of three alicyclic ketoximes has been rationalized on the basis of I-strain. Kinetic and activation parameters have been determined and a mechanism... 

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