Bond fissions

In a homoatomic bond, such as between two fluorine atoms, there is no permanent charge separation. If the bond in the fluorine molecule should break, what do you think would be the likely products Write an equation for your suggested answer. 

It is not unreasonable to suppose that the symmetrical fluorine molecule would break into two equal parts, each of which is a fluorine atom. What is the charge on each fluorine atom after the bond has broken, and how many electrons are there around each atom  

The charge is zero, and there are seven electrons around each atom. Using the principle of the Conservation of Charge the products must have a net zero charge, because that is the charge on the fluorine molecule. The fluorine atom has seven electrons in its valence shell, six of which exist in three lone pairs, while the last is an unpaired electron hence, the fluorine atom is a radical. 

Draw the appropriate arrows to represent the homolytic cleavage of the fluorine molecule. 

In this case, there are two arrows, each of which has its tail in the middle of the bond that is going to break. One arrow with half an arrowhead is going to one fluorine atom, while the other is going to the other. The half arrowhead indicates that only one electron is involved in each movement. This shows that the two electrons, which originally formed the single bond between the atoms, will be divided equally between the two fluorine atoms, with one electron going to each atom. 

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Troe J 1983 Specific rate constants k(E, J) for unimolecular bond fissions J. Chem. Phys. 79 6017-29... 

An anchor, as defined above, contains stable molecules, conformers, all pairs of radicals and biradicals formed by a simple bond fission in which no spin re-pairing took place, ionic species, and so on. Figure 1 shows some examples of species belonging to the same anchor. Thus, an anchor is a more general and convenient temi used in the discussion of spin re-pairing. 

Indene derivatives 264a and 264b are formed by the intramolecular reaction of 3-methyl-3-phenyl-l-butene (263a) and 3,3,3-triphenylpropylene (263b) [237]. Two phenyl groups are introduced into the /3-substituted -methylstyrene 265 to form the /3-substituted /3-diphenylmethylstyrene 267 via 266 in one step[238]. Allyl acetate reacts with benzene to give 3-phenylcinnamaldehyde (269) by acyl—O bond fission. The primary product 268 was obtained in a trace amount[239]. 

JOC1537). The mechanisms of these transformations may involve homolytic or heterolytic C —S bond fission. A sulfur-walk mechanism has been proposed to account for isomerization or automerization of Dewar thiophenes and their 5-oxides e.g. 31 in Scheme 17) (76JA4325). Calculations show that a symmetrical pyramidal intermediate with the sulfur atom centered over the plane of the four carbon atoms is unlikely <79JOU140l). Reactions which may be mechanistically similar to that shown in Scheme 18 are the thermal isomerization of thiirane (32 Scheme 19) (70CB949) and the rearrangement of (6) to a benzothio-phene (80JOC4366). 

Another mode of reductive ring cleavage is observed for 4-phenylazetidin-2-ones. These undergo N(l)—C(4) bond fission on hydrogenolysis in the presence of Raney nickel to yield the corresponding 3-phenylpropanamides (75S547 p. 583). 

Benzoxepin, 2,3,4,5-tetrahydro-applications, 7, 590 bond fission, 7, 549 synthesis, 7, 577... 

Discussion of acid and ester reaction mechanisms is often carried out in terms of the classification in Table 1-1. This specifies the type of bond fission (Ac or... 

This four-atom replacement was observed in some reactions of uracil derivatives, containing at position 5 a substituent with the CCCN moiety. Treatment of the Z-isomer 5-(2-carbamoylvinyl)-l,3-dialkyluracil with ethanolic sodium ethoxide gave in good yield 3-ethoxycarbonylpyridin-6(lf/)-one (84%) together with 3-A-methylcarbamoyl)pyridin-6-(l7 )-one (10%) (85JOC1513) (Scheme 26). The reaction involves an initial attack of the terminal amino group of the side-chain on position 6 of the uracil molecule. C-6-N-1 bond fission and N-C bond formation yield the pyridin-6(l//)-one. A subsequent attack of the ethoxide ion on the carbonyl groups of the side-chain yields both pyridin-2-one derivatives (Scheme 26). Similar results were obtained with the -isomer. 

The proposed mechanism is based on the basis of the fact that ylides (Scheme 23 and Scheme 24) undergo bond fission between the phosphorus atom and the phenyl group in TPPY as reported by Nagao et al. [51] and between the sulfur atom and the phenyl group in POSY as observed in triphenylsulfonium salts [52-55] when they are irradiated by a high-pressure mercury lamp. The phenyl radicals thus produced participate in the initiation of polymerization. 

Nitrating propane produces a complex mixture of nitro compounds ranging from nitromethane to nitropropanes. The presence of lower nitroparaffins is attributed to carbon-carbon bond fission occurring at the temperature used. Temperatures and pressures are in the range of 390°-440°C and 100-125 psig, respectively. Increasing the mole ratio of propane to nitric acid increases the yield of nitropropanes. Typical product composition for 25 1 propane/acid ratio is ... 

The octadehydrocorrins including the corroles are able to stabilize the electron pair liberated by the bond fission between the carboxylic group and the chromophore. 

If X-Y bond fission occurs, the product is a 6-coordinate iridium(III) complex (Table 2.6) otherwise a 5-coordinate (or pseudo-5-coordinate) adduct is obtained in which Ir formally retains the (+1) state (Table 2.7). This distinction can be somewhat artificial IrCl(02)C0(PPh3)2 can be regarded as an iridium(III) peroxo complex. 

The reaction for the oxidation of sulphoxides by peracids in an alkaline medium is probably best described as shown in equation (16). Here the addition step is usually much slower than the latter step due to the low O—O bond energy which allows easy bond fission. For the reaction in acidic media, equation (17) is probably a good representation. 

Sulfones are thermally very stable compounds, diaryl derivatives being more stable than alkyl aryl sulfones which, in turn, are more stable than dialkyl sulfones allyl and benzyl substituents facilitate the homolysis by lowering the C—S bond dissociation energy17. Arylazo aryl sulfones, on heating in neutral or weakly basic media at 100°C, yield an aryl and arenesulfonyl radical pair via a reversible one-bond fission followed by dediazoni-ation of the aryldiazenyl radical (see Scheme 2 below)20. However, photolysis provides a relatively easy method for generating sulfonyl radicals from compounds containing the S02 moiety. 

Thus we think of the chemical ionization of paraffins as involving a randomly located electrophilic attack of the reactant ion on the paraffin molecule, which is then followed by an essentially localized reaction. The reactions can involve either the C-H electrons or the C-C electrons. In the former case an H- ion is abstracted (Reactions 6 and 7, for example), and in the latter a kind of alkyl ion displacement (Reactions 8 and 9) occurs. However, the H abstraction reaction produces an ion oi m/e = MW — 1 regardless of the carbon atom from which the abstraction occurs, but the alkyl ion displacement reaction will give fragment alkyl ions of different m /e values. Thus the much larger intensity of the MW — 1 alkyl ion is explained. From the relative intensities of the MW — 1 ion (about 32%) and the sum of the intensities of the smaller fragment ions (about 68%), we must conclude that the attacking ion effects C-C bond fission about twice as often as C-H fission. 

By contrast in compounds 14, 15, and 16, from which MW — 43 also cannot be formed by single bond fission, the intensities of MW — 43 are negligibly small. For these we find that no feasible rearrangement process such as Equation 16 can be written. Thus for compound 14, for example,... 

In effect we postulate that the olefin ion is formed by a 1-3 hydride ion shift accompanied by a beta homolytic bond fission. The fact that olefin ions are formed only at branch points (except methyl branch points) could be explained on an energetic basis if it were not for the contrary fact that the over-all energetics are highly unfavorable. Thus in Reaction 20 we see that a disubstituted olefin ion is formed, and this will be true for any branch other than a methyl branch. Thus ... 

Figure 3. Difference mass spectrum of the [HO—Fe—CH3] insertion intermediate at photolysis wavelengths of 570 nm (a) and 350 nm (b). Simple Fe—C bond fission is observed at both wavelengths, but photolysis at 350 nm also triggers the half reaction to produce Fe+ + methanol (CH3OH).

All the oxidants convert primary and secondary alcohols to aldehydes and ketones respectively, albeit with a great range of velocities. Co(III) attacks even tertiary alcohols readily but the other oxidants generally require the presence of a hydrogen atom on the hydroxylated carbon atom. Spectroscopic evidence indicates the formation of complexes between oxidant and substrate in some instances and this is supported by the frequence occurrence of Michaelis-Menten kinetics. Carbon-carbon bond fission occurs in certain cases. 

A. Pentoses.—t-Ascorbic acid 2- and 3-phosphates, together with their phosphate esters, give a characteristic colour with ferric chloride and this colour reaction has been used in a study of the hydrolysis of L-ascorbic acid 3-phosphate (58). The acid-catalysed, pseudo-firsi-order hydrolysis proceeds with P—O bond fission, as does the bromine oxidation of its phenyl ester. Both of these observations can be rationalized if (58) is... 

Formate dehydrogenase can be said to catalyze a kind of decarboxylation reaction and is the most widely used in NADH regeneration. However, as the reaction does not include C—C bond fission, the studies on this enzyme are not described in this chapter. 

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