Ring production comparison

To the extent that cyclic transition-state strains parallel ring-product strains, the above considerations provide a proper guideline for prediction and interpretation of the oxygen-atom effect on rates of ring closure. This is clearly shown by a comparison of EM data for the two closely related ring-closure reactions (43) and (53a) in 75% aqueous ethanol (Illuminati et... 

Fig. 10. Comparison of ring production from pure (A) and sulfur containing (B) n-heptane with and without mixing of catalyst components (/I8a).

Analysis of Products. The three fractions collected from each sample were analyzed by gas chromatography. The noncondensable fraction, containing hydrogen and methane, was analyzed on silica gel at room temperature. The fraction containing C2-C4 hydrocarbons was analyzed at 75 °C. on silica gel treated with didecyl phthalate. Aliquots of the liquid fraction were analyzed on three columns of different selectivity Bentone-34-didecyl phthalate silicone SE-30 and m-polyphenyl ether (five-ring). Products were identified, and their yields were determined by comparison of retention volumes and peak areas with values for known amounts of authentic samples. 

In anthracene (123), there are three different positions (Cl, C2, and C9) and there are five different positions (Cl, C2, C4, C5, and C9) in phenanthrene (124). Electrophilic aromatic substitution of anthracene leads to substitution primarily at C9 because that gives an intermediate with the most resonance forms and the most intact benzene rings. A comparison of attack at Cl and at C2 in anthracene will show that there are more resonance forms for attack at Cl and more fully aromatic rings. Attack at C9 leads to an intermediate with even more resonance, and electrophilic substitution of anthracene leads to C9 and Cl products, with little reaction at C2. 

Propagation takes place by addition of n molecules of monomer to the alkoxyethanol product to form H-(0CH2CHR) -0C2H5. The rate constant for the reaction relative to ethylene oxide depends on the epoxide or, actually, the substituents on the oxirane ring. For comparisons of polymerization rates for substituted oxiranes, see Table 1. 

Yield of ring-opening products comparison of Pt-1 r/HY zeolite and Ni-Mo carbide catalysts. 

Because the product composition is kinetically controlled, the isomer ratio will be governed by the relative magnitudes of AG, AGI, and AG, the energies of activation for the ortho, meta, and para transition states, respectively. In Fig. 4.7 a qualitative comparison of these AG values is made. At the transition state, a positive charge is present on the benzene ring, primarily at positions 2, 4, and 6 in relation to the entering bromine. 

The chemical reduction of enamines by hydride again depends upon the prior generation of an imonium salt (111,225). Thus an equivalent of acid, such as perchloric acid, must be added to the enamine in reductions with lithium aluminum hydride. Studies of the steric course (537) of lithium aluminum hydride reductions of imonium salts indicate less stereoselectivity in comparison with the analogous carbonyl compounds, where an equatorial alcohol usually predominates in the reduction products of six-membered ring ketones. 

Mention must also be made of the neat series of reactions carried out by Wieland and Neeb which led to a number of ring extended products. These are summarized by the conversion of 406 into 406a and 407. The structure of 406a was confirmed by a comparison of its... 

Assignment of the l,2,4-triazolo[l,5-c]pyrimidine structures to the products obtained from the previously described cyclizations and not the alternative [4,3-c] structures has been rationalized and corroborated on the basis of (a) preference of cyclization at the more nucleophilic triazole ring N2 rather than at its less nucleophilic N4 (65JOC3601 88JMC1014), (b) inability of the obtained products to undergo acid- or base-catalyzed Dimroth rearrangement, a property characteristic of the thermodynamically less stable [4,3-c] isomers (91JMC281), (c) comparison with unequivocally prepared... 

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