Alkanes cyclic, molecular formula

The majority of marine isonitriles are sesquiterpenes with the molecular formula, C16H25N. Often cyclic, these are alkanes or alkenes possessing only a single isocyano-related functional group. In the mass spectrum, they exhibit a molecular ion at w/z 231, or an intense fragment ion at m/z 204, indicative of M+-HCN. Some are crystalline (see Table 2). With few exceptions most of the isothiocyano and formamido analogs are minor noncrystalline metabolites (see Table 3). 

Cycloalkanes are cyclic saturated hydrocarbons with the general formula C H2 . Therefore, a substance with the formula C3H8 could not be a cycloalkane, since C3H8 conforms to the general formula, C H2 +2, the molecular formula for an alkane. It is, however, too small to be a branched alkane with a methyl group attached to the longest chain. In fact, C3H8 is propane. 

Traditionally, the molecular formula of a compound was derived from elemental analysis and its molecular weight which was determined independently. The concept of the degree of unsaturation of an organic compound derives simply from the tetravalency of carbon. For a non-cyclic hydrocarbon i.e. an alkane) the number of hydrogen atoms must be twice the number of carbon atoms plus two, any deficiency in the number of hydrogens must be due to the presence of unsaturation, i.e. double bonds, triple bonds or rings in the structure. 

Cyclohexane, the six-carbon ring hydrocarbon with the molecular formula C6H12, is the most significant of the cyclic alkanes. Under ambient conditions it is a clear, volatile, highly flammable liquid. It is manufactured by the hydrogenation of benzene and is used primarily as a raw material for the synthesis of cyclohexanol and cyclohexanone through a liquid-phase oxidation with air in the presence of a dissolved cobalt catalyst. 

Alkenes are said to be unsaturated because they are capable of adding hydrogen in the presence of a catalyst. The product, an alkane, is called saturated because it cannot react with any more hydrogen. The presence of a pi bond of an alkene (or an alkyne) or the ring of a cyclic compound decreases the number of hydrogen atoms in a molecular formula. These structural features are called elements of unsaturation. Each element of unsaturation corresponds to two fewer hydrogen atoms than in the saturated formula. 

The properties of cyclohexane, for example, show clearly that it is an alkane. However, combustion analysis and molecular weight determination show its molecular formula to be C5H12. Only a cyclic structure (although not necessarily a six-membered ring) is consistent with both sets of data. 

In Chapter 2, you learned that the general molecular formula for a noncyclic alkane is C H2n+2- You also learned that the general molecular formula for a cyclic alkane is C H2 because the cyclic stmcture reduces the number of hydrogens by two. Noncyclic compounds are also called acyclic compounds ( a is Greek for non or not ). 

The general molecular formula for an acyclic alkene is also C H2 because, as a result of the carbon-carbon double bond, an alkene has two fewer hydrogens than an alkane with the same number of carbon atoms. Thus, the general molecular formula for a cyclic alkene must be C H2 -2- We can, therefore, make the following statement The general molecular formula for a hydrocarbon is C H2 +2, minus two hydrogens for every tt bond and/or ring in the molecule. 

Alkynes are hydrocarbons that contain a carbon-carbon triple bond. Because of its triple bond, an alkyne has four fewer hydrogens than the corresponding alkane. Therefore, the general molecular formula for an acyclic (noncyclic) alkyne is C H2 -2, and that for a cyclic alkyne is C H2 -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. 

Arts. This is a broader question than Problem 14.4. The molecular formula fits the general formula C H2 , which is one pair of hydrogens less than an alkane. There is one ring or one extra bond present in CjH O. We have the aldehyde and ketone shown in Problem 14.4 if the extra bond is in a C=0 group. If the extra bond is in a C=C group, we have three different alkene-alcohols and one alkene-ether. If there is a ring instead of an extra bond, we have two possibilities—a cycloalkane-alcohol and a cyclic ether. 

Give the molecular formula of a cyclic alkane, a cyclic alkene, a linear alkyne, and an aromatic hydrocarbon that in each case contains six carbon atoms. Which are saturated and which are... 

From what we have said so far, the formula C3H cannot represent an alkane. Not enough hydrogens are present to allow each carbon to form four bonds, unless there are multiple bonds. For example, the structural formula CH3—CH=CH2 fits the molecular formula but cannot represent an alkane because of the double bond. The C3H5 formula does become acceptable for an alkane if the carbon atoms form a ring, or cyclic, structure rather than the open-chain structure shown ... 

The alkanes are acyclic saturated hydrocarbons, and the cycloalkanes are cyclic saturated hydrocarbons. The simplest hydrocarbon, an alkane called methane, consists of one carbon atom to which four hydrogen atoms are bonded in a tetrahedral arrangement. You can represent methane by its molecular formula, CH4, which gives the number and kind of atoms in the molecule, or by its structural formula, which shows how the atoms are bonded to one another... 

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