Effects of Substitution

A study of the effect of substitution patterns in oxadiazoles and isoxazoles and their effect on the UV spectra in the lO -lO M concentration range was performed. Hypso-chromic effects and deviations from Beer s law were observed and were believed to be associated with antiparallel, sandwich-type self-association via dipole-dipole interactions. Beer s law is followed when the molecular dipole moments are small or when self-association is sterically hindered. 

To return to a more historical development the mercuric acetate oxidation of substituted piperidines (77) should be discussed next. This study established that the normal order of hydrogen removal from the aW-carbon is tertiary —C—H > secondary —C—H > primary —C—H, an observation mentioned earlier in this section. The effect of substitution variations in the piperidine series can be summarized as follow s l-mcthyl-2,6-dialkyl and 1-methyl-2,2,6-trialkyl piperidines, as model systems, are oxidized to the corresponding enamines the 1,2-dialkyl and l-methyl-2,5-dialkyl piperidines are oxidized preferentially at the tertiary a-carbon the 1-methyl-2,3-dialkyl piperidines gave not only the enamines formed by oxidation at the tertiary a-carbon but also hydroxylated enamines as found for 1-methyl-decahydroquinoline (48) (62) l-methyl-2,2,6,6-tctraalkyl piperidines and piperidine are resistant to oxidation by aqueous mercuric acetate and... 

The last of the procedures of preparation of A -alkyl derivatives of dioxotriazines is the cyclization of A-alkylated semicarbazones of a-keto acids. It was employed only in a few cases and it appears that its yields are very low. Despite the fact that even here a fundamental effect of substitution on the yield of cyclization can be expected, as the case is with analogous thiosemicarbazones (e.g., Section II,B,4,b), the method is of no particular preparative value. 

The rate of iodine formation depends on the degree of A"-substitu-tion. Compounds which are unsubstituted on both the iV-atoms (35) and those wdth a single A -substituent (43) liberate instantly the calculated quantity of iodine in the cold. However, the 1,2-disubstituted diaziridines (44) need brief heating with the acid iodine solution they then give 95-100% of the calculated iodine. " This effect of substitution is so well defined that it can be used for a proof of constitution. The diaziridino-triazolidincs (37) prepared from aldehydes, ammonia, and chloramine give complete iodine liberation only on heating. Thus the structure 57 which is isomeric with 37 can be eliminated. ... 

The effect of substitution of labile chlorines by acetoxy groups on the thermal stability of polymer taken in isolation appears to correspond to the thermal degradation behavior of VCA Ac copolymers over the whole composition range [136,137]. 

The effect of substitutents at the C3 and C6 positions of the azepine ring is much more dramatic in that they force the 1//-azepine into a competing [6 + 2] Tt-cydoaddilion at the Cl —Cl positions.6 1 In fact, at room temperature [6 + 2] cycloaddition by a kinetically controlled, non-concerted, ionic process appears to be dominant, since on treating a mixture of ethyl 3,6-dimethyl- and ethyl 2,5-dimethyl-l//-azepine-l-carboxylate with less than a molar equivalent of ethenetctracarbonitrile, only the [6 + 2] cycloadduct 10 of the 3,6-dimethyl-l//-azepine is formed. 

Similarly, examples of barriers arising largely from simple steric hindrance can be found, as for instance in the hindered diphenyls.35 On the other hand there are many arguments suggesting that this is not the important force in ethane and similar molecules. It would be difficult to understand the relatively slow fall in barrier from ethane to methyl silane to methyl germane on a van der Waals repulsion basis. Furthermore, the small effect of substituting F, Cl, or Br on one end would also seem mysterious. The equilibrium orientation in propylene is opposite to the predictions of one of the quantitative van der Waals theories. Finally, the apparently small effect of bending back the C—H bonds is not in accord with either the electrostatic or van der Waals pictures. 

Structure activity relationships, i.e., the total pattern of change in a biological activity as a function of chemical structure, typically derived from a comparison within a chemical series so that the biological effects of substitution at each structural position may be determined and correlated. 

Effect of Substituting BTNEEDNA for HMX in an EANF-Propellant Formulation... 

Fig. 4a,b. The effect of substitution of an alkoxy tail for an alkyl tail in cyanobiphenyls a transition sequence is K kf N b transition sequence is K N /... 

In the present study, we focus on the effects of substituting one of the protons by a deuteron. While giving only one isomer of the unionized molecule, this produces two inequivalent isomers of the Jahn-Teller distorted ion one isomer where the deuteron occupies one of the two sites on the C2 symmetry axes (Hj or H4) and one where it occupies one of the four equivalent remaining sites (H2, H3, H5 or H6). The effects on the ESR spectrum will below be illuminated both theoretically and experimentally. 

The operator 6 will denote the difference between an arbitrary and a standard reaction (2) i.e., the effect of substitution, solvent, etc. It is to be distinguished from A, which refers to the difference between the ground and final (transition) states. 

FIGURE 23 Rate of enzymatic surface erosion of a 1 1 copolymer of e-caprolactone and 6-valerolactone, crosslinked with a dilactone to form an elastomer. The effect of substitution of the e-caprolactone nucleus is also shown. (From Ref. 98). 

Katsuyama S, Tanaka Y, Hashimoto H, Majima K, Nagai H (1997) Effect of substitution of La by alkaline earth metal on the thermoelectric properties and the phase stability of y-La3S4.1 Appl Phys 82 5513-5519... 

With a view to determining the equilibrium constant for the isomerisation, the rates of reduction of an equilibrium mixture of cis- and rra/i5-Co(NH3)4(OH2)N3 with Fe have been measured by Haim S . At Fe concentrations above 1.5 X 10 M the reaction with Fe is too rapid for equilibrium to be established between cis and trans isomers, and two rates are observed. For Fe concentrations below 1 X lO M, however, equilibrium between cis and trans forms is maintained and only one rate is observed. Detailed analysis of the rate data yields the individual rate coefficients for the reduction of the trans and cis isomers by Fe (24 l.mole sec and 0.355 l.mole .sec ) as well as the rate coefficient and equilibrium constant for the cw to trans isomerisation (1.42 x 10 sec and 0.22, respectively). All these results apply at perchlorate concentrations of 0.50 M and at 25 °C. Rate coefficients for the reduction of various azidoammine-cobalt(lll) complexes are collected in Table 12. Haim discusses the implications of these results on the basis that all these systems make use of azide bridges. The effect of substitution in Co(III) by a non-bridging ligand is remarkable in terms of reactivity towards Fe . The order of reactivity, trans-Co(NH3)4(OH2)N3 + > rra/is-Co(NH3)4(N3)2" > Co(NH3)sN3 +, is at va-... 

While neurotoxic effects of amphetamines upon MA neurons had been reported in previous biochemical studies, a seminal paper from the University of Chicago has stimulated a new wave of interest in the neurotoxic effects of substituted amphetamines upon 5-HT projections. 

The main effect of substituting Ce by Zr is to increase the thermal stability of the materials in significant proportion. 

The effects of substitutents on the y-carbon on the efficiency of the type II cleavage are presented in Table 3.15.<89) These data indicate that the rate constant of cleavage increases as the strength of the y C—H bond decreases, that is, from a primary to a secondary to a tertiary hydrogen atom. The substitution of groups capable of radical stabilization, such as — or... 

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