Unsaturated noncyclic compounds

Structure Influence on the Rate of Hydrogenation of Unsaturated Noncyclic Compounds... 

In [5, 6] the emphasis of the authors was on the reactions of cyclic emanine 4 with some a,(3-unsaturated carbonyl compounds. These reactions involve both noncyclic chalcone 5 and arylidenecyclohexanones 7 (Scheme 3.3). The solvent used was acetonitrile and the duration of the reaction varied from 15 to 48 h. Zhang et al. [6] also showed that at room temperature the reaction of enamine 4 with unsaturated ketone 9 led to the isolation of 5-hydroxyhexahydroimi-dazo[l,2- ]pyridine 10 without further dehydration. Subsequently, compound 10 reacted with another equivalent of unsaturated ketone to yield a heterocyclic salt 11 (Scheme 3.4). 

What kind of structure might we predict for benzene if we knew only what the early chemists knew The molecular formula (CgHg) tells us that benzene has eight fewer hydrogens than an acyclic (noncyclic) alkane with six carbons (C H2 +2 = C6H14). Benzene, therefore, has a degree of unsaturation of four (Section 3.1). This means that benzene is either an acyclic compound with four tt bonds, a cyclic compound with three tt bonds, a bicyclic compound with two tt bonds, a tricyclic compound with one TT bond, or a tetracyclic compound. 

All the hydrocarbons we have met so far have the molecular formula C H.2 + 2-Because these molecules are linear or branched chains, we refer to them as either noncyclic or acyclic alkanes. Molecules of this formula are also called saturated hydrocarbons, which means that the carbon-carbon bonds in the molecule are all single bonds. There is a class of closely related molecules that shares most chemical properties with the noncyclic alkanes but not the general formula. These molecules have the composition C H2 and are the cycloalkane ring compounds mentioned briefly in Section 2.1. Cycloalkanes with this formula are also saturated. Molecules that have the formula C H2 but have no rings are called unsaturated hydrocarbons. Unsaturated compounds have carbon-carbon double (or triple) bonds and will be discussed in Chapter 3. 

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