In a previous report, we validated the use of a database that compiled the relative response factors of flavor and fragrance compounds under standard GC conditions for a flame ionization detector. Here we investigate the prediction of unknown response factors from the molecular structure by using combustion enthalpies. In a first step, this enthalpy was well-predicted with either ab initio calculation or multiple linear regression based on the molecular formula. In a second step, good correlation was observed between these combustion enthalpies and experimental relative response factors, and so the response factors were predictable from only the molecular formula. With a database of 351 compounds, about 60% of them exhibited a difference of less than 5% between the predicted and experimental relative response factors and about 80% exhibited a difference of less than 10%.

Alkyl or aryl a-keto esters of primary or secondary alcohols decompose upon irradiation at 350 ± 370 nm from the intermediate triplet state into aldehydes or ketones in polar, as well as apolar solvents. The use of these keto esters as delivery systems for the controlled release of perfumery aldehydes and ketones was investigated by photoirradiation in the presence of oxygen with a Xe or UV lamp, as well as outdoor sunlight. Systematic GC/ MS analysis of the irradiated solutions showed that, under these conditions, the desired Norrish type-II fragmentation of the ester side chain is the predominant reaction pathway in most of the cases. g-H Abstraction from the alkyl side chain of alkyl keto esters, as well as an intramolecular PaternoÁ-Büchi reaction or epoxidation of the alkene function in different citronellyl a-keto esters were identified as the most important side reactions. Some of the experimental findings have been rationalized on the basis of ab initio and density-functional calculations. (Cyclohexyl)oxoacetates and oxo(phenyl)acetates were found to be the most suitable precursors for the desired perfumery applications.1. Introduction. ± Aldehydes and ketones are important classes of fragrances that are present in all kinds of perfumes. However, many of them are very volatile and can, after application, only be perceived over a relatively short period of time. Furthermore, as constituents of perfumes for a variety of different bodycare or household applications, such as shampoos, soaps, all purpose cleaners, fabric softeners, or detergent powders, they are often too hydrophilic and thus easily carried away by water during various rinsing processes instead of staying on substrates like hair, skin, or fabrics.To prolong the desired odor perception of this class of compounds, we have prepared a series of photolabile, hydrophobic, non-volatile fragrance precursors as potential delivery systems for the controlled release of perfumery aldehydes and ketones in typical bodycare and household applications. In this publication, we describe the fragrance release from a-keto esters upon irradiation with artificial light sources, as well as natural sunlight in the presence of O 2 [1]. Some interesting fragrances for release in functional perfumery are depicted in Fig. 1 [2].The photolysis of alkyl or aryl a-keto esters of primary or secondary alcohols has been intensively studied since the early sixties [3 ± 7]. It was found that these esters decompose from their intermediate triplet state into aldehydes or ketones upon irradiation at 350 ± 370 nm in polar, as well as apolar solvents [7 ± 11]. Most of the photoirradiations described in the literature were carried out in degassed solutions in the absence of O 2 . The relatively good yields of the fragmentation process have allowed the use of a-keto esters as intermediates for the transformation of primary or secondary alcohols to aldehydes and ketones, respectively [12].

Abstract. In order to analyze the relationships among 32 descriptors of odors (notes), similarity coefficients were calculated using a data bank of 628 odoriferous products. The simple examination of the similarity matrix (32,32) has shown notes selectively and strongly associated (e.g. camphoraceous -pincy and musky-powdery) and others less selectively associated (e.g. floral, green and herbaceous). This analysis was completed by four multivariate statistical methods. Non-linear mapping (NLM) proved to be more efficient than principal coordinates analysis for planar representation of olfactory notes, and has given results similar to those previously obtained using other data and other methods (similar disposition of notes around the central note 'floral'). Furthermore, the ascending hierarchical taxonomy and the minimal spanning tree were coherent with the NLM representation. These three methods complete each other and constitute a convenient system to analyze odor descriptions.

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We previously showed that the relative response factors of volatile compounds were predictable from either combustion enthalpies or their molecular formulae only 1. We now extend this prediction to silylated derivatives by adding an increment in the ab initio calculation of combustion enthalpies. The accuracy of the experimental relative response factors database was also improved and its population increased to 490 values. In particular, more brominated compounds were measured, and their prediction accuracy was improved by adding a correction factor in the algorithm. The correlation coefficient between predicted and measured values increased from 0.936 to 0.972, leading to a mean prediction accuracy of ± 6%. Thus, 93% of the relative response factors values were predicted with an accuracy of better than ± 10%. The capabilities of the extended algorithm are exemplified by (i) the quick and accurate quantification of hydroxylated metabolites resulting from a biodegradation test after silylation and prediction of their relative response factors, without having the reference substances available; and (ii) the rapid purity determinations of volatile compounds. This study confirms that Gas chromatography with a flame ionization detector and using predicted relative response factors is one of the few techniques that enables quantification of volatile compounds without calibrating the instrument with the pure reference substance.