Organic Chemsitry

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By knowing the natural abundance of minor isotopes, it's possible to calculate the relative heights of M+ and M+1 peaks. If natural abundances are 12C - 98.9% and 13C - 1.10%, what are the relative heights, to the nearest 0.1%, of the M+ and M+1 peaks in the mass spectrum of ribose, C5H10O5?

Ignore the contributions of isotopes like 2H (deuterium; 0.015% natural abundance) and 17O (0.04% natural abundance) that are small.

I initially just substituted 13 for 12 when calculating the molar mass but that didn't work. How else should I go about this problem.

  • Organic Chemsitry -

    Wouldn't that be 98.9 to 1.10? That is, on a scale of 100, C 12 will be 98.9 and C 13 will be 1.10. That is a ratio of 98.9/1.10 = 89.9:1

  • Organic Chemsitry -

    5.5 is the answer

  • Organic Chemsitry -

    Hey Saj how did you get 5.5 as the answer?

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