Unsaturation number

A double bond decreases the number of hydrogen atoms in a molecule by two compared to the corresponding alkane. The general formula of a noncychc alkene is, compared to the 

Determine the number of hydrogen atoms in an alkane with the same number of carbon atoms. 

Subtract the actual number of hydrogen atoms in the compound from the number in the alkane. 

Divide the difference by two to obtain the d ree of imsaturation, or unsaturation number. The following formula gives the numerical result. 

The unsaturation number of 3-bromo-l-propene, obtained by substitution into the above formula, is 1. 

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Elisabethol (13) [4] shows the same stereochemistry as the pseudopterosin aglycone 10. Elisabatins A-C (14,15,16) [ 14] have the same amphilectane skeleton found in the aglycone portion of the pseudopterosins. The elisabatins are unique among the amphilectane-type diterpenoids because they possess an unusually high unsaturation number that leads to extended aromatic conjugation. 

There are two ways to solve this problem. The first is the use of a classical unsaturation number that can be obtained from the empirical formula, as one is taught in freshman chemistry courses. Comparison of the atomic composition of starting materials and products yields the unsaturation number balance that one needs to assess oxidation level changes as a whole. Frequently, however, it is also useful to learn the way by which parts of the molecule undergo oxidation level changes in order to concentrate one s attention on that particular portion of the compound. This leads us to discuss the second way of solving the oxidation level problem. 

Among the first proposed simple multiple bond descriptors [Pellegrin, 1983], there are the number of unsaturation sites (US) defined as the number of double bonds plus the number of triple bonds in the molecule, that is, US = DB + TB, and the unsaturation number (UN) defined as the number of double bonds plus twice the number of triple bonds, that is, UN=DB + 2 X TB. Moreover, the same author proposed the degree of unsaturation (DU) by also considering the number of rings C (the —> cyclomatic number), that is, DU= DB + 2 X TB + C= UN + C. 

Unsat index multiple bond descriptors Unsat-p index multiple bond descriptors unsaturation index multiple bond descriptors unsaturation number multiple bond descriptors unsaturated bonds multiple bond descriptors... 

It is important to realize, that within a certain lipid class there is still a very large number of individual lipid molecules, which can be formed by a great variety of combinations of two fatty acids differing in their chain length (carbon number), in unsaturation (number of C=C bonds) and in their position on the glycerol backbone (Cl or C2). For simplicity, fatty acids are often denoted by the number of carbon atoms number of C=C bonds, e.g. 18 0 for stearic, 18 1 for oleic/elaidic, 18 2 for linoleic, 18 3 for linolenic acids, etc. Any chemical manipulation on lipids of natural origin usually involves simultaneous reactions of quite a few similar but not identical substrate molecules. On the other hand, individual lipids may have specific biological role which -at least in principle- could be assessed by a selective chemical transformation or removal of a lipid of particular composition. 

It was found from the analysis of laboratory cultures and field samples that the extent of unsaturation (number of double bonds) in these long-chain ketones varies linearly with growth temperature of the algae over a wide temperature range (Brassell et al. 1986 Prahl and Wakeham 1987). To describe this, an unsaturation index was suggested, which in its simplified form is defined by the concentration ratio of the two... 

The oils used to make alkyds are selected on unsaturation number. In general, the higher the unsaturation number, the better drying. Excellent drying oils for alkyds include soybean, linseed, tung, and dehydrated castor oils. 

Over 100 naturally occurring fatty acids are known. They vary in chain length and degree of unsaturation (number of double bonds). Nearly all have an even number of carbon atoms. Most consist of linear chains of carbon atoms, but a few have branched chains. Fatty acids occur in very low quantities in the free state and are foimd mostly in an esterifled state as components of other lipids. 

Partial structures a and b account for seven degrees of unsaturation, which suggests that an additional ring might be present in order to obtain an unsaturation number of 8. Combination of the fragment a and b leads to the basic skeleton shown below. 

Capillary GC-MS is useful for identifying the carbon and unsaturation number of acylglycerols. However, APCI LC-MS can be used to analyze less volatile acylglycerols that may be unsuitable for GC-MS. APCI LC-MS has become the method of choice for qualitative and quantitative analysis of acylglycerols and, when combined with MS/MS, is capable of distinguishing fatty acid chains in the sn-2 position from those in the sn-1/3 positions. 

D 3030 VOLATILE MATTER OF VINYL CHLORIDE RESINS D 3045 HEAT AGING OF PLASTICS WITHOUT LOAD D 3124 VINYLIDENE UNSATURATION NUMBER BY FTIR D 3291 COMPATIBILITY OF PLASTICIZERS/COMPRESSION D 3349 ABSORPTION COEFFICIENT/PE CARBON BLACK D 3351 GEL COUNT OF PLASTIC FILMS... 

Figure 12.1 illustrates a MALDI-IM MS spectrum of 200 pmol of porcine brain PS extract in negative ion mode with DHA (2,6-dihydroxyacetophenone) matrix. In this spectrum, five PS species are observed. As shown in Figure 12.1, as the degree of unsaturation (number of double bonds) on the acyl chain increases, the ion mobility drift time decreases. This is most likely due to the fact that the presence of a double bond causes the acyl chain to bend, making it more compact and thus causing a smaller ion collision cross section and a decrease in mobility time. This result was previously observed in positive ion mode for phospholipids by MALDI-IM and ESI-IM MS.< ... 

Three important attributes of the structure of these fatty acids are The length of the fatty chain, the degree of unsaturation (number of... 

All grades of regular butyl rubber are tacky, rubbery, light amber colored solids, manufactured by copolymerizing isobutylene with less than 3% isoprene. Double bonds introduced into the macromolecule by isoprene permit the polymer to be crosslinked or vulcanized. Though butyl rubber is unsaturated relative to poly isobutylene, its 0.8-2.1 mole % unsaturation (number of isoprene units per hundred monomer units in the polymer chain) is still far less than the 100% unsaturation of natural rubber or the 60-80% unsaturation of SBR. This... 

Degree of unsaturation (number of rings + number of tt bonds) is calculated from the molecular formula by using the equation... 

Calculate the unsaturation number for each of the following compounds. 

Squalene, an intermediate in the biosynthesis of steroids, has the molecular formula Hydrogenation yields a compound with molecular formula What is the unsaturation number of... 

Answer The unsaturation number is 6. Squalene does not have any rings. 

Selmi, B., Gontier, E., Ergan, F., and Thomas, D. (1998) Effects of fatty acid chain length and unsaturation number on triglyceride synthesis catalyzed by immobilized lipase in solvent-free medium. Enzyme Microb. Technd., 23, 182-186. 

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