Relative activity effect

In general, the reactions are second-order, first-order with respect to both nucleophile and substrate (17). The relative activating effects of various substituents have been determined (18) to be in the order ... 

Protons attached to sp carbons are more acidic than protons attached to nonallylic sp carbons. Also, the inductive effect of a heteroatom further increases the acidity of an adjacent sp C-H bond, facilitating a-lithiation. The relative activating effect of heteroatoms is sulfur > oxygen > nitrogen. Thus, treatment of 2-ethoxy-l-(phenylthio)ethylene with t-BuLi results in exclusive lithiation at the phenylthio substituted carbon. ... 

The variation in Na-K ATPase activity with pH and with Na K ratio is shown in Figures 3 and 4. Although some differences are apparent in the curves obtained with the various divalent cations, the qualitative behavior is the same for all. However, the relative activating effect is pH dependent. The patterns of activity variation in Figures 3 and 4 could be duplicated using controls that contained choline acetate instead of Na+-K+ acetate and ouabain, and so they do not reflect variations in degree of ouabain inhibition. No activating effect under the conditions studied could be found for Ba2+, Ca2+, Cd2+, Cu2+, Fe2+, Pb2+, or Sr2+. 

A comparison of the activities of these three alkaloids lias been made by Graliam and Gunn using their antagonism to the effects of carbamjd-choline chloride on isolated mammalian intestine. The relative activities found were, atropine sulphate 1 I-hyoscyamine sulphate 2-4 hyoscine hydro bromide 1-5. The results of previous authors are discussed and reasons suggested for some of the differences found. 

Cushny has compared the action of d- and Z-hyoscyamines with that of atropine, and of d-homatropine with that of dZ-homatropine in antagonising the action of pilocarpine, and finds that the order of activity of the first three is in the ratio 1 40 20, and of the second two in the ratio 4 2-5. He drew attention also to the important influence of the acyl radical in the tropeines, which exercises the maximum effect when it is a hydroxyalkyl aromatic residue and is laevorotatory and in illustration of this point gives the following table of relative activities on the basis of capacity to antagnonise pilocarpine in the salivary fistula dog —... 

Canadine is bitter and in small doses causes drowsiness and depression. In large doses it gives rise to transient excitement succeeded by depression and paralysis of the central nervous system. Its injection is followed by violent peristalsis with diarrhoea. It is said to have no effect on the blood pressure. The pharmacological action of canadine a- and -meihochlorides was examined by Laidlaw, who found both to have the curare-like action common to ammonium bases, the -isomeride being the more active the relative activities of the four optically active forms are given as h da. ip dp = 1 Q 2 28. 

The effect of change in the spatial relations at C and C is not clear since, as explained above, there is doubt as to the relative activities of the components of the two pairs, quinine and quinidine, and cinchonidine and cinchonine, but epf-C -quinine and epi-C -quinidine are only slightly active or, according to Dirscherl and Thron, inactive. This result supports Neeman s view that for anti-malarial activity the direction of rotation must be the same at C and C but that does not explain the... 

FIGURE 14.12 The effect of temperature on enzyme activity. The relative activity of an enzymatic reaction as a fnncdon of tempera-tnre. The decrease in the activity above 50 C is dne to thermal denatnradon. 

The effect of a substituent may be substantially modified by fast, concurrent, reversible addition of the nucleophile to an electrophilic center in the substituent. Ortho- and para-CS.0 and pam-CN groups have been found by Miller and co-workers to have a much reduced activating effect on the displacement of halogen in 2-nitrohaloben-zenes with methoxide ion [reversible formation of hemiacetal (143) and imido ester anions (144)] than with azide ion (less interaction) or thiocyanate (little, if any, interaction). Formation of 0-acyl derivatives of 0x0 derivatives or of A-oxides, hydrogen bonding to these moieties, and ionization of substituents are other examples of reversible and often relatively complete modifications under reaction conditions. If the interaction is irreversible, such as hydrolysis of a... 

Relative reactivity of ring-positions based on positional selectivity of polychloro-azines must be regarded with caution because of the unequal activating effects of the chlorine substituents on each other. Also, it should be emphasized that one cannot use the positional selectivity in di- and tri-substitutions to assess relative reactivity of different positions. In such substitutions, the reactivity is determined by a complex combination of activating and deactivating effects which are unequal at the ring-positions (cf. Sections II, E, 1, II, E, 2,c, and II,E,2,e). 

Where ortho effects and special entropy factors control the relation of the reaction rates, it seems more appropriate to evaluate relative activation from the energies of activation. 

Reaction of 2,4,7-trichloroquinoline with sodium methoxide (65°, 30 min) yielded an equal mixture of 2,7-dichloro-4-methoxy- (40%) and 4,7-dichloro-2-methoxy-derivatives (31%). The activating effect of the chloro groups is evident from the inertness of 4-chloro-quinoUne to methoxide ion at 65°. Alteration of the relative reactivity by cationization of the azine ring is again noted here in the acid-catalyzed hydrolysis (dilute HCl, 100°, 1.5 hr) of the trichloro compound to give 72% of the 2-hydroxylation product.Similarly, acid-hydrolysis of the alkoxy group proceeds much more readily in 2-ethoxy-4-chloro- than in 4-ethoxy-2-chloro-quinoline. ... 

Tliis interpretation is based only upon the structural and electronic properties of the pyridinium cations. Tire calculation of relative activation Ijarri-ers for the competing substitution reactions will give more reliable results —especially if solvent effects are included in the calculations. In order to assess the reliability of actual theoretical methods as applied to model sys-... 

The diffusion current Id depends upon several factors, such as temperature, the viscosity of the medium, the composition of the base electrolyte, the molecular or ionic state of the electro-active species, the dimensions of the capillary, and the pressure on the dropping mercury. The temperature coefficient is about 1.5-2 per cent °C 1 precise measurements of the diffusion current require temperature control to about 0.2 °C, which is generally achieved by immersing the cell in a water thermostat (preferably at 25 °C). A metal ion complex usually yields a different diffusion current from the simple (hydrated) metal ion. The drop time t depends largely upon the pressure on the dropping mercury and to a smaller extent upon the interfacial tension at the mercury-solution interface the latter is dependent upon the potential of the electrode. Fortunately t appears only as the sixth root in the Ilkovib equation, so that variation in this quantity will have a relatively small effect upon the diffusion current. The product m2/3 t1/6 is important because it permits results with different capillaries under otherwise identical conditions to be compared the ratio of the diffusion currents is simply the ratio of the m2/3 r1/6 values. 

Table VI. Effect of Particle Size on Relative Activity...

Nesmeyanov et a/.545 used a mixture of ferrocene, deuterated trifluoroacetic acid and benzene in the molar ratios 1 2 20 in a preliminary investigation of the reactivity of ferrocene and its derivatives. At 25 °C, rate coefficients were 1,620 x 10-7 (ferrocene) and 19.3 xlO-7 (acetylferrocene). In a subsequent publication by Alikhanov and Shatenshtein543 these values were altered to 1,600 x 10-7 and 1.5 x 10 7, respectively, and a value of 0.77 x 10"7 added for 1,1-diacetylferrocene. Under the same conditions, toluene gave a value of 0.3 x 10-7 so that the activating effects of these compounds relative to benzene can be approximately determined. 

At low pH the existence of HOCl is favoured over OCl" (hypochlorite ion). The relative microbiocidal effectiveness of these forms is of the order of 100 1. By lowering the pH of hypochlorite solutions the antimicrobial activity increases to an optimum at about pH 5 however, this is concurrent with a decrease in stability of the solutions. This problem may be alleviated by addition of NaOH (see above equation) in order to maintain a high pH during storage for stability. The absence ofbuffer allows the pH to be lowered sufficiently for activity on dilution to use-strength. It is preferable to prepare use-dilutions of hypochlorite on a daily basis. 

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