Alkane odor intensity

This indicates that log P can be used to reproduce predictive equations. The aldehyde-ketone results indicate that the bulkiness of the substituents on the carbonyl group does not determine the level of odor intensity. Suprathreshold correlations indicate that the polar effects of the groups bonded to the carbonyl group does not determine the level of odor intensity. Similar conclusions regarding the importance of hydrophobic and steric effects can be made from the alkane odor intensity -log P and E equations in Table III. 

Pentane is a colorless, flammable liquid (the first liquid member of the alkanes) that is lighter than water. It has a pleasant odor that can be detected at 900 ppm, and a moderate odor intensity is observed at 5000 ppm. It occurs as two other isomers, including isopentane [(CH3)2CHCH2CH3] and neopentane [C(CH3)4]. Isopentane (2-methylbutane) apparently has physical and physiological characteristics similar to straight-chain pentane. Neopentane (2,2-dimethylpropane) is similar to butane in physical and physiological characteristics. In air, one part per million of C5 pentane is equivalent to 3 mgm. ... 

The use of log P and HB parameters as a tool for predicting odor intensity seems promising. Although many excellent correlations were obtained as presented in Tables I-V further studies are needed to investigate several unresolved areas. The question on whether log P is linearly or parabolically related to odor intensity for a specific medium needs to be resolved. Six equations in Tables 1-V linearly related log P to odor intensity, while five parabolic relationships were observed which had an optimum hydrophobicity (log P) associated with maximum odor intensity. Log Po values observed were 3.17 and 2.90 for alcohols (threshold-aic). Alkanes had a log Po value of 5.33 (threshold-air). In aqueous media alcohols had a log Po value of 3.98 while 3-alkyl-2-methoxy pyrazines had a value of 2A3. The animal data indicates that rats had log Po values of 5.90 for acetates and 7.91 for alcohols. 

The examples presented in Fig. 5.1 show that the exponent n and, therefore, the dependency of the odor intensity on the concentration can vary substantially. Within a class of compounds, the range of variations is not very large, e. g., n = 0.50—0.63 for the alkanals C4-C9. 

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