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Showing posts with label diethyl ester. Show all posts
Showing posts with label diethyl ester. Show all posts

Saturday 22 November 2014

Pentanedioic acid, diethyl ester



Pentanedioic acid, diethyl ester


In this spectrum the two methyls labeled (a) are homotopic, as are the two methylenes labeled (b).
  • The three Hs within each methyl are homotopic, and the two Hs within each methylene are enantiotopic.
  • Hence we get single absorptions for these groups, displaying the typical ethyl pattern of methyl triplet and CH2 quartet.
  • Note the numerical values for the integration shown under the chemical shift scale, which fit the 3 : 2 ratio of CH3 to CH2.
The two CH2 groups labeled (c) are homotopic (enantiotopic within the group) and therefore have the same chemical shift.
  • They are split to a triplet by the CH2 at (d).
The two Hs of (d) are enantiotopic and have the same chemical shift.
  • With a total of four equivalent neighbors (both (c) groups), (d) should be a quintet. The enlarged view shows this clearly.
  • The apparent small additional couplings seen are probably artifacts. The integration values fit the 2 : 1 ratio of (c) to (d).
Part of the use we make of nmr spectra is simple pattern recognition. An ethyl is always triplet + quartet, although the separation between the two groups will vary according to the rest of the structure. A chain of three CH2 with no other neighbors is always triplet + quintet, again with variation in the separation on the chemical shift axis.