Entering the data
DP4 requires one set of experimental data plus the calculated data for each of the candidate structures. It can work with either 13C data or 1H data, but the best results
are produced when both carbon and proton data are available.
The experimental and computational data should be typed into the boxes at the top of the applet as follows:
Calculated shifts should be entered separated by commas in the form of a matrix. For example:
The first row gives the atom labels (these can be anything you like, provided the same labels are used for the experimental shifts) and each subsequent row gives the calculated shifts for each of the candidate structures; in this case the calculated shifts for two candidate structures have been entered. The calculated shifts are specified in the same order as the labels, so for example in this case the calculated shift of C1 in the first structure is 202.2 ppm and the calculated shift of C2 in the second structure is 45.7 ppm.
Experimental shifts should be entered as list of shifts separated by commas with assignments (optional) in brackets. For example:
200.5(C1), 45.5(C2), 14.8(C3), 16.4 (C4)
The assignments (in brackets) tell the program which experimental shifts it may match up with which calculated shifts. If no assignments are given, i.e.
50.7, 45.5, 14.8, 16.4
the program will match the experimental shifts up in order with each set of calculated shifts so as to get the best match. In this case this would mean that the 16.4 ppm shift is assigned to C4 in isomer 1 but C3 in isomer 2. Partial assignments are allowed, for example:
50.7(C1), 45.5(C2), 14.8(C3 or C4), 16.4(C3 or C4)
In this case the program will fix the assignment of C1 and C2 but will swap the C3 and C4 shifts as necessary to give the best match. This again means that the 16.4 shift is assigned to C4 in isomer 1 but C3 in isomer 2, and vice versa for the 14.8 shift.
It is important to ensure that it is always possible for the program to make an assignment. For example,
50.7(C1 or C2), 45.5(C2), 14.8(C3), 16.4(C4)
is not valid because if the 50.7 shift is assigned to C2 in a particular isomer (because C2 happens to have the highest calculated shift in that isomer) then no assignment can be found for the 45.5 shift. In this case the entry should be amended to
50.7(C1 or C2), 45.5(C1 or C2), 14.8(C3), 16.4(C4)
50.7, 45.5(C2), 14.8(C3), 16.4(C4)
(where the lack of assignment for the 50.7 shift indicates that this shift may be assigned to any carbon) is not valid because the 50.7 shift might be assigned to C2 (or C3 or C4) leaving no assignment left for the 45.5 shift (or whichever corresponds to the atom the 50.7 shift is to be assigned to).
Commas may be used in place of the word "or" in the brackets, eg. 14.8(C3,C4) is equivalent to 14.8(C3 or C4)
The order in which the shifts are entered is not important as the program will automatically sort them into descending order for its analysis.
Once the data has been entered, clicking on Read Data causes it to be read into the program; any errors detected in the input are then reported. Next, either:
- Make sure that the experimental peaks have been matched up with the right calculated peaks: step 3
- Calculate DP4, trusting that the computer has made the right assignment: step 4
Assigning Stereochemistry to Single Diastereoisomers by GIAO NMR Calculation: The DP4 Probability
S. G. Smith and J. M. Goodman J. Am. Chem. Soc. 2010, Accepted