O-F bond energy

Tihe currently accepted value of the O—F bond energy (45 kcal./mole) is calculated from the standard heat of formation of OF2 (7.6 kcal./mole) which was based on an average of three values obtained in 1930 (7, 8) the precision of which was quite poor. To determine a more reliable heat of formation of OF2 and thus a better O—F bond energy, the heat of reaction of the following system was measured ... 

The heat of formation value, combined with the most recent heats of atomization of fluorine (18.860 keal.) and oxygen (59.559 keal.) (7, 8) yields a value of 50.7 kcal./mole for the O—F bond energy in OF2. 

Using data in Appendix K, calculate the average O—F bond energy in OF2(g). 

Because of the high C - F bond energy, glycosyl fluorides are stable in comparison to the other glycosyl halides, and this character has attracted much attention. They have been prepared in many different ways. One of them, rather classical, is through addition of the elements of HF (for example, HF in benzene ), BrF, or IF to per-O-acylated glycals. ... 

Table 3 Energy partitioning analysis of the N-N, C-O and B-F bonds. Energy valnes are given in kcalmoC ...

The retardation of the reaction with chlorine (which reacts with CF3 to form CF3CI) makes it possible to study step (1). Stewart and Cady found that for this step, A = 1.33 X 10 exp (—25,000/ 7 ) l.mole sec . Porter and Cady (refs. - ) estimated a energy of 47 kcal.mole for the O-F bond in trifluoro-methyl hypofluorite, from equilibrium studies at 367-467 °C in the system... 

Activation energies of 46.2 and 45.0 kcal mol have been derived for steps 1 and 6, respectively these values lead to bond dissociation energies i)°(CH30—OCH3) = 46.7 0.8 kcal mol-i and Z)°(CH80—F) = 44.5 0.8 kcal mol" for the central O—O bond in bistrifluoromethyl peroxide and the O— F bond in trifluoromethyl hypofluorite, respectively. ... 

Quantum chemical calculations indicate that the barriers to internal rotation in FOOF are much higher than in HOOH the energies of the planar syn and anti forms are both calculated to be about 100 kJ moP above that of the equilibrium structure[6]. Interestingly the 0-0 bond distances in the planar forms are similar to the 0-0 bond distance in HOOH while the O-F bond distances are similar to the O-F bond distance in OF2. 

Once the number of valence electrons has been ascertained, it is necessary to determine which of them are found in covalent bonds and which are unshared. Unshared electrons (either a single electron or a pair) form part of the outer shell of just one atom, but electrons in a covalent bond are part of the outer shell of both atoms of the bond. First-row atoms (B, C, N, O, F) can have a maximum of eight valence electrons, and usually have this number, although some cases are known where a first-row atom has only six or seven. Where there is a choice between a structure that has six or seven electrons around a first-row atom and one in which all such atoms have an octet, it is the latter that generally has the lower energy and that consequently exists. For example, ethylene is... 

There are two kinds of bond energy. The energy necessary to cleave a bond to give the constituent radicals is called the dissociation energy D. For example, D for H2O—>HO -f H is 118 kcal mol (494kJmol ). However, this is not taken as the energy of the O—H bond in water, since D for H—O H -f O is 100 kcal... 

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