Bromination compared

Chapter 4, the absorption cross sections of the major sources of bromine to the stratosphere, CH3Br, CBrClF2 (Halon-1211), and CBr3F (Halon-1301), are substantial well out into the 250-nm region. The C-Br bond is even weaker than the C-Cl bond, as is generally the case for bromine compared to chlorine bonds (e.g., Lee et al., 1999a). For example, the C-Br bond strength is 70 kcal mol-1 versus 85 kcal mol-1 for C-Cl and 110 kcal mol-1 for C-F the C-Br bond breaks first ... 

The assumption that PBBs and PBDEs share many toxicological characteristics with PCBs also does not consider geometrical differences due to the higher atomic weight and considerably larger molecular volume of bromine compare to chlorine (Hardy 2000, 2002). These differences contribute to dissimilar physical/chemical properties that can influence the relative toxicokinetics and toxicities of the chemicals. 

E. Wasserman (DuPont Experimental Station, U.S.A.). One of the particularly exciting things about C60Br6 to us was the unexpected presence of the pair of bromines on adjacent carbons (unlike C60Br24). (i) Please comment on the stability of the pairing of bromines compared with C60Br8 (ii) Do they dimerize ... 

Consider the halogens chlorine, bromine, and iodine. The melting point and boiling point of chlorine are — 101.0°C and —34.6°C while those of iodine are 113.5°C and 184.4°C, respectively. Thus chlorine is a gas and iodine is a solid under room conditions. Estimate the melting point and boiling point of bromine. Compare your values with those from a handbook of chemistry. 

What is the color of liquid bromine (10) Is it a comparatively volatile liquid (11) What is the evidence (12) How does it compare with chlorine in this respect Pour 5 c.c. of water into the test tube containing the bromine. (13) What is the density of liquid bromine compared with water (14) What is the evidence as to its solubility Drop a small piece of litmus paper into the bromine and water. (15) What was the action on the litmus (16) What other element acts in the same way ... 

These reactions have been summarised in Table 8.3 (refs.21-28) and often indicate the known more selective nature of bromination compared with chlorination. 

Energy diagrams for the first propagation step of chlorination and bromination, comparing the difference in transition states leading to primary, secondary, or tertiary radicals. 

Molecules such as hydrogen bromide are permanently polar because of the higher electronegativity of bromine compared with hydrogen. The mechanism of electrophilic... 

A series of four oxyanions of bromine, comparable to the series for chlorine discussed in the text, also exists. Write the formulas and names for the four oxyanions of bromine. 

While gas phase chemistry leads to much higher levels of active bromine compared to chlorine, this is even more the case for iodine. Solomon et al. suggested that iodine might be of importance in ozone depletion. At present there is no information on the amounts of iodine in the stratosphere, but heterogeneous reactions will probably not play a significant role. Conversely, fluorine is almost completely in its deactivated form HF, and also heterogeneous reactions have been found to be immeasurably slow. Hence, fluorine species are not expected to influence stratospheric chemistry. 

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