Molecular Formulas and Degrees of Unsaturation

Problem 9.17 Compare the molecular formulas of (a) //-hexane and c>do-hexare (b) //-pentane and c>cIopentane (c) 1-hexene and cydohexene (d) dodecane, n-hex>lcyclohexane, and c>cIohcx>lcydohcxanc. (c) In general, how can you deduce the number of rmgs in a compound from its molecular formula and degree of unsaturation ... 

On the basis of the molecular formula, the degree of unsaturation for a hydrocarbon is calculated as (2m -I- 2 — n) / 2, where m is the number of carbons and n is the number of hydrogens. The number calculated is the number of rings and / or 7T bonds. For molecules containing heteroatoms, the degree of unsaturation can be calculated as follows ... 

PeDegrin, V. (1983) Molecular formulas of organic compounds. The nitrogen rule and degree of unsaturation. J. Chem. Educ., 60, 626-633. 

The empirical-formula routine uses the isotopic abundances and the inferred molecular mass and functional groups to currive at upper limits for carbon content and degree of unsaturation. 

In general, each ting or double bond in a molecule corresponds to a loss of two hydrogens from the alkane formula ChH2/1+2- Knowing this relationship, it s possible to work backward from a molecular formula to calculate a molecule s degree of unsaturation—the number of rings and/or multiple bonds present in the molecule. 

Let s assume that we want to find the structure of an unknown hydrocarbon. A molecular weight determination on the unknown yields a value of 82, which corresponds to a molecular formula of CfcHjo Since the saturated Q alkane (hexane) has the formula C61-114, the unknown compound has two fewer pairs of hydrogens (H]4 - H l() = H4 = 2 H2), and its degree of unsaturation is two. The unknown therefore contains two double bonds, one ring and one double bond, two rings, or one triple bond. There s still a long way to go to establish structure, but the simple calculation has told us a lot about the molecule. 

B The hormone cortisone contains C, H, and O, and shows a molecular ion at M+ = 360.1937 by high-resolutiou mass spectrometry. What is the molecular formula of cortisone (The degree of unsaturation of cortisone is 8.)... 

Obtain a secure molecular formula, and calculate the degree of unsaturation. 

In this book, in order that you can concentrate your attention on the NMR spectra, we shall provide you with the molecular formula in all cases. This in turn provides you with information which can be extremely useful during the process of solving the structure if the molecule only contains C, H, N and O then you can use the molecular formula to obtain the number of so-called double bond equivalents, i.e. information on the degree of unsaturation. Though there are various formulas which can be devised to do this, we recommend the calculation using the following formula for a molecule CaHbOcNd, the number of double bond equivalents DBE is calculated as follows... 

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. 

After these 3 steps, the molecular formula is reduced to CnHm and the degree of unsaturation is given by ... 

Compound 58 was isolated as a yellow crystalline, optically active compound. HREIMS data for 58 gave a molecular formula of C15H16O4 with an inherent eight degrees of unsaturation. The IR spectrum was consistent with the presence of conjugated carbonyl functionalities including a y-lactone (1779 cm ) and a conjugated ketone (1665 cm ). The... 

The IR absorption indicates that C is an alcohol. From M+, we can arrive at a molecular formula of C5H10O, which indicates one degree of unsaturation. The broadband-decoupled spectrum shows five peaks two are due to a double bond, and one is due to a carbon bonded to an electronegative atom (O). 

Compound A is a hydrocarbon with M+ = 78. What is its molecular formula What is its degree of unsaturation Draw three possible formulas for A. The 13C NMR spectrum of A shows 3 peaks - at 18.5 8, 69.4 8 and 82.4 8, and the XH NMR spectrum shows two peaks. What is the structure of A What significant absorptions would you see in the IR spectrum of A ... 

The molecular weight of Compound A shows that the molecular formula of A is C5H10O (one degree of unsaturation), and the IR absorption shows that A is an aldehyde. The uncomplicated H NMR is that of 2,2-dimethylpropanal. 

SsmpiG ProblGm 10.1 Calculate the number of degrees of unsaturation in a compound of molecular formula C4H6, and... 

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