Bond lengths carbon-halogen

Table 6.1 Carbon-Halogen Bond Lengths, Bond Strength and Dipole Moment...

Since the size of halogen atom Increases as we go down the group in the periodic table, fluorine atom is the smallest and iodine atom, the largest. Consequently the carbon-halogen bond length also Increases from C—to C— I. Some typical bond lengths, bond enthalpies and dipole moments are given in Table 10.2. 

The carbon-halogen bond lengths increase as the halogen atoms become bigger (larger atomic radii) in the order... 

In spite of the absence of many examples, the ascending sequence for primary, secondary and tertiary carbon-halogen bond lengths is apparent thus, for C—Cl bonds, CHaCHjCK/i = 1.788 0.002 A), >... 

Table 2.4 Carbon-Halogen Bond Lengths and Bond Strengths ...

TABLE 6.1 CARBON-HALOGEN BOND LENGTHS AND BOND STRENGTHS... 

Halogen atom size increases as we go down the periodic table fluorine atoms are the smallest and iodine atoms the largest. Consequently, the carbon-halogen bond length increases and carbon-halogen bond strength decreases as we go down the periodic table (Table 6.1). Maps of electrostatic potential (see Table 6.1) at the van der Waals surface for the four methyl... 

A carbon-halogen bond in the monomer, polymer or solvent is always a centre of transfer reactions. Transfer to monomer controls chain length in polyvinyl chloride so efficiently that the molecular mass of the products is independent of the amount of initiator over a rather wide concentration range [35], Also, vinylidene chloride lowers the polymerization degree of its own polymer by transfer [36]. 

The carbon-halogen bonds of aryl and vinyl haltdes are unusually short. In chlorobenzene and vinyl chloride the C—Cl bond length is only 1.69 A, as compared with a length of 1.77-1.80 A in a large number of alkyl chlorides (Table 25,2). In bromobenzene and vinyl bromide the C—Br bond length is only 1.86 A, as compared with a length of 1.91-1.92 A in alkyl bromides. 

Interaction between the Oxygen p-type Lone Pair and Adjacent q-bonds The interaction between the oxygen p-type lone pair and the adjacent antibonding orbital of a carbon-halogen bond was first considered in 1959 by Lucken as a possible explanation of the abnormally low NQR frequencies of Ot-haloethers (33). Later on, Altona showed that the same phenomenon could explain the peculiarities of some bond lengths in similar compounds (2). The spectroscopic properties of pyranose sugars which we have described in the first two sections of this article seem to imply that the existence of such an interaction lies beyond all possible doubt in these molecules. It does not follow that they can explain the Anomeric Effect (34) (35). For this, we need a quantitative estimation of the stabilization introduced in a molecule by such interactions. 

Halogen compounds with more than two reactive carbon—halogen bonds afford star polymers, the arm number of which is defined by the number of the initiating sites, whereas the arm length therein is determined simply from the initial molar ratio of monomer to initiator. The multifunctional initiator method gave various star polymers with 3 (MI-27 to MI-33), 4 (MI-34 to MI-42), 5 (MI-43), 6 (MI-44 to MI-50), 8 (MI-51 and MI-52), and 12 arms (MI-53 and MI-54). 

Several pyranosyl halides have been studied as acetylated or benzoylated derivatives. In both the fluorides and chlorides, the equatorial carbon-halogen bonds are shorter than the axial bonds, with the data for fluorides illustrated in Fig. 14. The C - F bond-lengths in both derivatives of -D-xylo-pyranosyl fluoride are significantly shorter than the 143.2 pm found for the non-anomeric C-F bond in l,3,4-tri-C -acetyl-2-deoxy-2-fluoro-D-xylo-pyranose. There is also a variation of 4.4 pm in the C-1 - 0-5 bond-lengths. 

Table 35.1 Bond lengths, van der Waals radii and total size of carbon halogen bonds.

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