O-halogen bonds

The broken bonds (boldface = dissociated atom or group) BDEs (boldface = recommended data reference in parentheses) Methods (reference in  

Methyl hypochlorite CI-OCH3 48.0 200.8 Derived from AfH in ref. 1994N1ST 

Dichlorine dioxide Cl-OOCl 21.8 91.2 Derived from AfH° in ref. 1994NIC/FRI 

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Figure 54 X-Ray single-ciystal structure of the 1 1 complex between stilbazoles and 4-iodotetrafluorophenol showing the I- -O halogen bond.

Alternatively, a chloride anion [88] can prevail over the carbonyl oxygen of the l,2-benziodoxol-3(l/()-one moiety and enter preferentially the iodine atom. The formed I O halogen bond is strong enough to drive the formation of heteromeric two component systems (Fig. 14) [89]. 

Zou WS, Han J, Jin WJ (2009) Concraitration-dependent Br "O halogen bonding between carbon tetrabromide and oxygen-containing organic solvents. J Phys Chem A 113 10125-10132... 

Fig. 5 Detail of the 1 1 CIO4 salts with EDT-TTFI2 Q ft) and tTTF-I (right) showing the I- O halogen bonds and the face-to-face interaction between radical species...

The carbon that bears the functional group is sp hybridized m alcohols and alkyl halides Figure 4 1 illustrates bonding m methanol The bond angles at carbon are approximately tetrahedral as is the C—O—H angle A similar orbital hybridization model applies to alkyl halides with the halogen connected to sp hybridized carbon by a ct bond Carbon-halogen bond distances m alkyl halides increase m the order C—F (140 pm) < C—Cl (179 pm) < C—Br (197 pm) < C—I (216 pm)... 

The latter is an exttemely reactive species. Trifluoroacetate is a good leaving group and facilitates cleavage of the O—Br bond. The acyl hypohalites are also the active halogenating species in solutions of the hypohalous acids in carboxylic acids, where they exist in equilibrium. 

R.A. More O Ferrall, in The Chemistry of the Carbon-Halogen Bond, S. Patai, Ed. Wiley-Interscience, Part 2, Chapter 9,609-675, (1973). 

Bonds become weaker as we move down the periodic table. Compare C—O and C—S or the four carbon-halogen bonds. This is a consequence of the first generalization, since bond distances must increa.se as we go down the periodic table because the number of inner electrons increases. 

The (EDT-TTF-I)2Br salt described above [36] and the 1 1 (TTFI4)I salt reported by Gompper [51] were the only structurally characterized salts with simple halide anions until Imakubo recently described an extensive series of Cl" and Br" salts from several ortho-diiodo tetrathiafulvalene, tetraselena-fulvalene and dithiadiselenafulvalene derivatives (Scheme 8) [62], The X-ray crystal structure analysis of the nine salts described there show a variety of halogen bonded motifs, demonstrating the adaptability of the supramolecu-lar interactions to other structural requirements imposed by the nature of the heteroatoms (O, S, Se) in the TTF frame. Indeed, in (EDT-TTF-l2)2X-(H20)2 (X = Cl, Br), a bimolecular motif (Fig. 6) associates two partially oxidized EDT-TTF-I2 molecules with one Br" anion and one water molecule. 

N- lomoallylic enamides 239 derived from pymvate were subjected to free radical cyclization in presence of R3SnH and AIBN. The radical species generated from the C-halogen bond homolytic cleavage underwent a 5-endo-cyclization followed either by a 5-exo- or 6-fV/z/o-cyclization and reduction of the final radical species (Scheme 63)... 

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