Mass differences between molecular formulas

How close are the exact masses of molecular formulas to one another We generate all molecular formulas from up to exact mass m = 500. There are 84,204,768 such molecular formulas. We order the exact masses in increasing order 

Then we calculate the differences between successive masses, as well as their minima, maxima and arithmetic means for the integer meiss ranges j m with Oj 0  

Further, we are interested in how far apart the closest exact molecular mass of other molecular formulas is, for each molecular formula. For this purpose we define the minimal mass differences (MMD)  

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It is therefore important to acquire data of the highest accuracy if unequivocal molecular compositions are to be determined. As a general rule, any molecular formulae for which the error (i.e. the difference between measured and theoretical masses) is greater than 10 ppm should be discounted. 

In calculating the exact masses of the three isotopomers of the peak M+1 (molecular formulae given in Part One), a = 209.09217 b = 209.095054 and c = 209.09321 amu. The differences between these values are very much smaller than the value of AM calculated from the spectrum. Under the conditions of recording the spectrum these three types of molecules would appear superimposed. 

The highest-resolution mass spectra are obtained by Fourier transform ion cyclotron resonance mass spectrometry.34 Molecular ions of two peptides (chains of seven amino acids) differing in mass by 0.000 45 Da were separated with a 10% valley between them. The ions each have a mass of 906.49 Da and a width at half-height of 0.000 27 Da. Compute the resolving power by the 10% valley formula and by the half-width formula. Compare the difference in mass of these two compounds with the mass of an electron. 

MO bond order One-half the difference between the numbers of electrons in bonding and antibonding MOs. (336) model (also theory) A simplified conceptual picture based on experiment that explains how an aspect of nature occurs. (9) molality (m) A concentration term expressed as number of moles of solute dissolved in 1000 g (I kg) of solvent. (403) molar heat capacity (C) The quantity of heat required to change the temperature of I mol of a substance by 1 K. (187) molar mass [M) (also gram-molecular weight) The mass of 1 mol of entities (atoms, molecules, or formula units) of a substance, in units ofg/mol. (72)... 

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