CD bonds

An unstable lower oxidation stale is found in Cd - CdCl and Cd - CdCl - AICI3 melts and may contain Cd — Cd bonds. The common co-ordination number for Cd is 6 (octahedral) although 4 and 5 co-ordination are known. 

Cyclodextrin stationary phases utilize cyclodextrins bound to a soHd support in such a way that the cyclodextrin is free to interact with solutes in solution. These bonded phases consist of cyclodextrin molecules linked to siUca gel by specific nonhydrolytic silane linkages (5,6). This stable cyclodextrin bonded phase is sold commercially under the trade name Cyclobond (Advanced Separation Technologies, Whippany, New Jersey). The vast majority of all reported hplc separations on CD-bonded phases utilize this media which was also the first chiral stationary phase (csp) developed for use in the reversed-phase mode. 

Appllca.tlons. The first widely appHcable Ic separation of enantiomeric metallocene compounds was demonstrated on P-CD bonded-phase columns. Thirteen enantiomeric derivatives of ferrocene, mthenocene, and osmocene were resolved (7). Retention data for several of these compounds are listed in Table 2, and Figure 2a shows the Ic separation of three metallocene enantiomeric pairs. P-Cyclodextrin bonded phases were used to resolve several racemic and diastereomeric 2,2-binaphthyldiyl crown ethers (9). These compounds do not contain a chiral carbon but stiU exist as enantiomers because of the staggered position of adjacent naphthyl rings, and a high degree of chiral recognition was attained for most of these compounds (9). 

Although reaction of carbonyl anions with group-IIB salts is seldom used to prepare derivatives of Zn and Cd, it works when used. Compounds containing Mo—Cd and W—Cd bonds can be synthesized by reacting aq Cd(CN)2 with dry Na[M(CO)3Cp-tj5] (M = Mo, W) ... 

We represent the four-atom problem in terms of diatom-diatom Jacobi coordinates R, the vector between the AB and CD centers of mass, and rj and r2, the AB and CD bond vectors. In a body-fixed coordinate system [19,20] with the z-axis chosen to R, only six coordinate variables need be considered, which we choose to be / , ri, and ra, the magnitudes of the Jacobi vectors, and the angles 01, 02, and (j). Here 0, denotes the usual polar angle of r, relative to the z-axis, and 4> is the difference between the azimuthal angles for ri and r2 (i.e., a torsion angle). 

Taylor PB, Ashman S, Baddeley SM, Bartram SL, Battle CD, Bond BC, Clements YM, Gaul NJ, McAllister WE, Mostacero JA, Ramon F, Wilson JM, Hertzberg RP, Pope AJ, Macarron R (2002) J Biomol Screen 7 554... 

AB and CD denoted the center positions of the bonds formed by atoms A and B and C and D respectively. La and Ly represent the lone pair positions. As we will see, this formulation takes into account bonds and lone pairs hybridation, each one of the term depending of an overlap functional. N0CC(AB) and Nocc(CD) are the electron occupation numbers of the AB and BC bonds. Therefore, Nocc is equal to 2 for usual bonds and lone pairs. R, i .ci) is the distance between the barycenters of the AB and CD bonds. 

Carbene adducts of dimethylcadmium 188-190 have been obtained by simple addition of CdMe2 to the corresponding carbene at room temperature.2 9 All the three adducts have similar structures. In the case of 190, the Ccarbene-Cd bond of 2.33 A is 0.15 A longer than the Cmethyi-Cd bonds of 2.18 A (Figure 28). As a result, the cadmium atom is in a distorted trigonal-planar environment with a Cmethy -Cd-Cmethyl angle of 136°. 

The above spectral densities can be modified for the occurence of chain flexibility, and for the director being oriented at dLD w.r.t. the external BQ field in the L frame. For CD bonds located in the flexible chain, the effect of DF is reduced due to an additional averaging of the time dependent factor (/f g) by conformational transitions in the chain. Consequently, the spectral densities given in Eqs. (60)-(62) are modified by replacing Soc%0(Pm,q) by the segmental order parameter YCD of the C-D bond at a particular carbon site on the chain.146,147 As observed experimentally,148,149 the spectral densities in a flexible chain show a SqD dependence when DF dominate the relaxation rates. The general expression of Jm(co 0LD) due to DF in uniaxial nematic phases is given by... 

It is well established that the average lengths of CH bonds are consistently 0.003 to 0.004 A longer than the corresponding CD bonds in the ground vibrational state (see Fig. 12.1, its caption, and Section 12.2.3). It remains only to establish the dipole moment derivative, (9p/9r), at the equilibrium bond length. That is available from theoretical calculation or spectroscopic measurement (via precise measurements of IR intensities of vibration-rotation bands). Calculations based on Equation 12.7 yield predicted dipole moment IE s in reasonable agreement with experiment. 

The CD bond stretching VCD spectrum of 24 consists of three negative features between 2150 and 2250 cm that can be attributed to the lone CD stretching mode for the two chair conformations, one with an axial CD bond and the other with an equatorial CD bond, with additional intensity arising from a Fermi enhanced overtone or combination mode. The FPC model predicts VCD intensities in this region three orders of magnitude below the experimental values. 

For (-)-cyclohexanone-2,6-chair conformations are equivalent, with the axial and equatorial CD bonds chirally oriented. The CD stretching VCD, positive at —2200 cm and negative between 2130-2170 cm , is consistent with that predicted for coupled motion of the two CD bonds. In this case, the splitting between the modes is due to different CD bond force constants for the axial and equatorial positions. 

Similar conclusions attend the insertions of CCI2 (from the thermolysis of ClsCCOONa at 120 °C) into a-deuteriocumene and cumene in which the primary fen/feo = 2.6, similar to Seyferth s finding with 32, and the p-secondary kinetic isotope effect is 1.20-1.25 for six deuteriums. Here, hyperconjugation at the p-CH (CD) bonds is thought to stabilize the partial cationic charge at the reaction center in transition state 33. 

Figure 2.2 Definition and sign convention for dihedral angle ft). The bold lines are the projections of the AB and CD bonds into the bisecting plane. Note that the sign of a> is independent of whether one chooses to view the bisecting plane from the AB side or the CD side...

Table 2 gives chromatographic data for different classes of enantiomeric dmgs resolved by P-CD bonded phases (8). Drugs for which resolution factors (R) greater than 1.0 were obtained include mephenytoin, ketoprofen, chlorpheniramine, and the barbiturates mephobarbital and hexobarbital. Cyclodextrin-bonded phases provide a rapid and specific technique for the pharmacological evaluation of racemic dmgs. 

The chirality of (15 )-2-adamantanone-4-13C (87) and (lS )-2,4-adamantanedione-4-13C (88) is solely due to 13C substitution. Since the 13C ring carbon of 87 is located in a positive octant, from the negative Cotton effect of 87, it follows that 13 C makes a smaller contribution than 12C. Diketone 88 exhibits three CD bonds with remarkably large amplitudes, which were attributed to different n - tt transitions195. 

CDs bonded to polymer-based gel) Keystone ft-OH and Keystone / -PM YMC Chiral cyclodextrin BR,... 

In another study [71], native and chemically modified -CD-bonded stationary phases of six types were evaluated for the chiral resolution of some... 

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