How to calculate new IHD after finding a molecule in IR spec

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SUMMARY

The discussion focuses on calculating the Index of Hydrogen Deficiency (IHD) after identifying functional groups in organic molecules, specifically using the example of C5H10O. The initial IHD calculation yields 1, and the user explores how to adjust this value after determining the presence of a ketone. The consensus is that for ketones and aldehydes, one should subtract CO from the molecular formula to find the new IHD, while for carboxylic acids and esters, CO2 should be subtracted, and for amides, CON is used.

PREREQUISITES
  • Understanding of Index of Hydrogen Deficiency (IHD) calculations
  • Familiarity with functional groups in organic chemistry, such as ketones and aldehydes
  • Knowledge of molecular formulas and their components
  • Basic skills in interpreting infrared (IR) spectroscopy data
NEXT STEPS
  • Study the calculation of IHD for various functional groups in organic chemistry
  • Learn about the structural characteristics of ketones and aldehydes
  • Research the implications of IHD in predicting molecular structure
  • Explore the use of IR spectroscopy in identifying functional groups
USEFUL FOR

Chemistry students, organic chemists, and anyone involved in molecular structure analysis will benefit from this discussion, particularly those interested in IHD calculations and functional group identification.

AMan24
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Homework Statement


Lets say i have C5H10O.. The IHD is (5x2+2-10)/2 = 1 IHD

So now i use my IR chart and i determine i have ketone

Now i want to find the new IHD and also figure out what other atoms i have left. So i need to subtract C5H10O by ketone and figure out the new IHD.

Homework Equations


Given formula: CcHhNnOoXx

IHD = 0.5 * [2c+2-h-x+n]

3. The Attempt at a Solution
So for ketone, my guess would be either subtracting CO from the original formula or subtracting C2H3O then calculating the new IHD which would be either

C5H10O - C2H3O = IHD 0.5 which doesn't make sense
C5H10O - CO = IHD 0, which does make sense, but is it correct

And you might say i don't need to calculate it for this problem, but i just want to know for in the future because for some problems finding the new IHD is useful...

My question is: What am i supposed to subtract exactly? And not just for this example but, let's say i have aldehyde, do i just subtract the CO or do i subtract CHO
 
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AMan24 said:
C2H3O

?
 
Borek said:
?

Isn't that was ketone is? A CO and a CH3 = C2H3O
 
Try to draw a C2H3O molecule.
 
Borek said:
Try to draw a C2H3O molecule.

I think i might have figured it out. So for ketones and aldehydes, its just CO. For carboxylic acids and esters its CO2. For amides its CON.. and so on
 

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