Benzoic acid, specific energy

As discussed earlier in Section lOC.l, ultraviolet, visible and infrared absorption bands result from the absorption of electromagnetic radiation by specific valence electrons or bonds. The energy at which the absorption occurs, as well as the intensity of the absorption, is determined by the chemical environment of the absorbing moiety. Eor example, benzene has several ultraviolet absorption bands due to 7t —> 71 transitions. The position and intensity of two of these bands, 203.5 nm (8 = 7400) and 254 nm (8 = 204), are very sensitive to substitution. Eor benzoic acid, in which a carboxylic acid group replaces one of the aromatic hydrogens, the... 

In a careful study of HH, HD, and DD transfer, Sakota and Sekiya [54] showed convincingly that the transfer is concerted, contradicting earlier conclusions [55], and that HD transfer contains two components due to the fact that the coupling between the monomers is small (about 3.5 cm i) compared to the energy shift for NH—>ND substitution (about 40 cm i), so that the excitation is effectively localized on one of the monomers in the mixed (i.e. dj) isotopomer, a situation similar to that encountered in dimeric benzoic acid and in 2PY-2HP. Specifically, they found that H D transfer is faster than HD transfer, where the asterisk indicates the monomer on which the excitation is localized. By analogy to the 2PY-2HP... 

The energy equivalent of the calorimeter, (calor) is defined as the amount of energy required to increase the temperature of the calorimeter by 1 K. The most precise determination of (calor) is based on the transfer of a determined quantity of electrical energy through a heater placed at the same location as the combustion crucible. Because most of the calorimeters used are of the isoperibol type and are not equipped for electrical calibration, a standard reference material, benzoic acid, is used. Its certified energy of combustion in O2 must have been measured in an electrically calibrated calorimeter. Because the conditions under which the specific energy of combustion reported on the certificate was determined usually differ from those ones used in combustion calorimeters, certain corrections must be applied [31]. Details of these corrections are given in the certificate. 

Respiration is generally regarded as the source of energy necessary to support life. That this is true does not need verification in an advanced treatise, but one specific case may be cited. Borsook and Dubnoff (14) have found that the synthesis of hippuric acid from glycine and benzoic acid can occur only in the presence of intact liver cells. Extracts and minced tissues do not suffice, which leaves but the one conclusion, that the respiration of living tissue is the source of the energy. 

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