Halogenation optical rotation

Optical rotation data have been used in two different ways to study tautomerism. The rate of racemization at an optically active carbon atom gives an upper limit for the rate at which the other tautomeric form is produced rates of halogenation and deuteration can sometimes be used in a similar way. 

Similarly, methyl a-chloroethyl ketone, a, -dichloroacetone and a,a,/3-trichlorobutyraldehyde have been converted phytochemically and in good yield to the corresponding primary or secondary halogenated alcohols. Since all these alcohols show optical rotation, it seems established that the phytochemical reduction generally takes an asymmetric course. (See pp. 80, 81, 88 and 92.)... 

Tables II to X give the melting points and, where applicable, the optical rotations of the inositols, inososes, inosamines, and quercitols, and of all of their known O-substituted derivatives. Anhydroinositols, although not substitution products in the strict sense, are included, as are the carbonyl-functional derivatives of the inososes. Halogen- and nitro-substituted cyclitols, and the C-methyl-inositols and their derivatives, are not included most of these compounds are referred to in the text. The derivatives are arranged in the following order salts (inosamines) or functional derivatives (inososes), carboxylic esters, borates, nitrates, sulfonic esters, phosphates, glycosides, acetals (and Schiff bases), ethers (and IV-alkyl derivatives), and anhydrides.

The optical rotations of the products show that all of these reactions are stereoselective. By the following reaction cycle, it can be proved that reaction 30a - 32a proceeds with retention of configuration of the metal center. Starting with the (—)365-methyl compound 31a, the (-l-ias-bromo complex 32a can be arrived at in two ways in a one-step or a two-step reaction. Consequently, the Fe—C bond in 31a can be directly cleaved by Br2, or it can first be cleaved by I2, and then, in a second step, the corresponding (-)365-iodo derivative 30a can be converted into the (-)365-bromo compound 32a. If the same stereochemistry for the cleavage of the Fe—C bond in 31a by the halogens Br2 and I2 is assumed, the transformation step (-)385-iodo compound 30a - (-)365-bromo compound 32a must necessarily occur with retention of configuration (58). 

Another numerical relationship involving the optical rotations of the poly-O-acetylglycosyl halides has been deduced by Brauns, who has summarized the results obtained after many years of precise observation on carefully purified materials. Brauns has shown that, in a number of cases, the differences of the specific rotations of the acetohalogeno derivatives of a sugar are directly proportional to the differences in the atomic radii of the halogen atoms. That is, for a given sugar the differences of the specific rotations (acetochloro — acetofluoro), (acetobromo — acetochloro), (ace-... 

The first aeetylated glycosyl fiuoride derivative was prepared by Brauns in 1923 and, in subsequent papers, he explored the synthesis of a number of poly-O-acetylglycosyl fluorides. In addition, Brauns prepared the other poly-O-acetylglycosyl halides of the same carbohydrates and investigated the proportionality relations which exist between their optical rotations and the diameters of the respective halogen atoms. ... 

Infrared spectroscopy has broad appHcations for sensitive molecular speciation. Infrared frequencies depend on the masses of the atoms iavolved ia the various vibrational motions, and on the force constants and geometry of the bonds connecting them band shapes are determined by the rotational stmcture and hence by the molecular symmetry and moments of iaertia. The rovibrational spectmm of a gas thus provides direct molecular stmctural information, resulting ia very high specificity. The vibrational spectmm of any molecule is unique, except for those of optical isomers. Every molecule, except homonuclear diatomics such as O2, N2, and the halogens, has at least one vibrational absorption ia the iafrared. Several texts treat iafrared iastmmentation and techniques (22,36—38) and thek appHcations (39—42). 

In the rest of this section we discuss our analysis (10,11) of the accurate cumulative reaction probabilities for the halogen-hydrogen halide systems that were published by Schatz (17-19). The CRPs were digitized with an optical scanner, which introduces negligible error. The accurate N°(E) was fit with cubic splines and convoluted using Eq. (20). Our analysis is based on the observation that the calculated CRPs of Schatz for Cl + HC1,1 + HI, and I + DI appeared to have an overall steplike structure reminiscent of that associated with quantized transition states, underlying the narrower features associated with trapped-state resonances and rotational thresholds. Our conclusion that quantized transition states exert broad control of the chemical reactivity for these reactions is not inconsistent with Schatz s description of the narrow trapped-state resonance and rotational threshold features. These different sorts of dynamical features represent different time scales, with the shorter-time (broader) features being more closely related to the traditional concern of chemical kinetics, i.e., reactivity, as discussed below Eq. (23). The relationship of features in the CRP to features in the photoelectron spectrum is not fully worked out yet. 

Figure 7.5 Experimental setup for the overview absorbance measurements with the ARES spectrograph (1) D2 lamp, (2) tungsten halogen lamp, (3) beam combiner, (4) mechanical shutter, (5,9) toroidal mirrors, (6) sample and blank reservoir, (7) magnetic valve, (8) flame atomizer, (10) entrance slit, (11 -14) pre-dispersing illumination optics, (15,18) spherical mirrors, (16) prism, (17) echelle grating, (19) CCD array detector, (20) Ne lamp, (R1-R5) piezo-electrically controlled rotation units...

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