Monoterpenes specific compounds

None of the monoterpene pheromones of bark beetles is represented by a specific compound per se however, species specificity of the signal is accomplished by qualitatively and quantitatively fine-tuned mixtures including enantiomeric proportions. 

Several lines of evidence support the conclusion that allelopathic inhibition of germination and plant growth typically occurs from the joint action of several allelochemicals. Additive or synergistic effects have been shown in bioassays with combinations of monoterpenes, organic acids, and several classes of phenolic compounds. These experiments demonstrate that a specific compound may be present below its threshold for inhibition and still be active in allelopathic interference by its effect in concert with other allelochemicals. 

B. frereana and B. papyrifera olibanum have very different terpenic composition from the others. B. frereana olibanum contains the same monoterpenes as olibanum from B. carteri, B. sacra or B. serrata, but is very poor in sesquiterpenes and contains none of the diterpenic biomarkers cited before. Two unidentified compounds (55 and 56) seem to be specific and the main diterpenes, present in high level, are four dimers of a-phellandrene. Dimer 3 (113) is the major component. On account of its absence in the other olibanum samples, it can be considered as characteristic of B. frereana olibanum. 

The desired citrus flavor is the result of volatile compounds in specific proportions. Citrus oils have unique composition profiles depending on the cultivar, the processing conditions, and the storage conditions. There have been more than 200 different compounds identified in citrus oils. However, the degree of unsaturation in monoterpenes leads to rapid oxidation and unstable compounds. The reactivity and volatility of citrus oils require strict quality control protocols. 

Monoterpenes are widely used as substrates in the development of new synthetic reagents and routes. However, many of these studies refer to a one-off use of a particular compound as one of many models and such are not discussed here unless of especial interest. We rather review the salient work involving specific functionalization and modification of the class. 

The reactions of metal complexes of monoterpenes continue to be actively explored and many specific examples will be found in later sections. Of general interest are the dimerization of 7r-allyl-Pd complexes of a- and p-pinenes and of carvone that are effected by irradiation at 366 nmM and the thermal decompositions of (TC-allyl)nickel halide complexes of, e.g., isoprene (33), to form myrcene.95 Hydrosilylation of 1,3-dienes e.g. isoprene, myrcene, ocimene) was found to be a regiospecific 1,4-addition for Pd complexes but followed the alternative route for Rh compounds a good discussion is appended.96 A series of dimers of isoprene... 

It has been understood for some time that none of the known free volatile monoterpenes of the grape is responsible for the specific flavor of muscats (18,19). Etievant et al. (91) recently drew attention to this point, but were unsuccessful in identifying compounds which could account for all the nuances of muscat flavor. 

A modern approach to dealing with insect pests that wreck crops is to use specific attractants to lure the pest to its doom while offering no threat to beneficial creatures. Compounds such as grandisol 34 are not themselves toxic but they are irresistible to specific insect pests. Grandisol, marketed as grandlure , an attractant for male cotton boll weevils, is one of a family of unusual monoterpenes containing a four-membered ring. Others are lineatin 35, an attractant for ambrosia beetles that bore into conifers, filifolone 36, and raikovenal 37 (a sesquiterpene). 

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