Pople notation

With the addition of polarization functions and/or diffuse functions to the basis sets, the Pople notation can become rather cumbersome. For example, the 6-311++G(3df,2pd) set has a single zeta core and triple zeta valence shell, diffuse functions for all the atoms. Regarding polarized functions, there are three sets of d functions and one set of f functions on the non-hydrogens and two sets of p functions and one set of d orbitals on the hydrogens. 

With an understanding of simple first-order spin systems and of the Pople notations, we can consider the following example. 

The concept of chemical shift equivalence is central to NMR spectrometry. Chemical-shift equivalent (isochronous) nuclei comprise a set within a spin system (Pople notation, Section 3.5). 

If two protons in the same set (i.e., chemical-shift-equivalent protons in the same multiplet) couple equally to every other proton in the spin system, they are also magnetically equivalent, and the usual Pople notations apply A2, B2, X2 etc. However, if two protons in a set are not magnetically equivalent, the following notations apply AA, BB, XX, etc. To rephrase Two chemical-shift-equivalent protons are magnetically equivalent if they are symmetrically disposed with respect to each proton in the spin system. Obviously magnetic equivalence presupposes chemical-shift equivalence. In other words, do not test for magnetic equivalence unless the two protons in question are chemical-shift equivalent. 

In summary At 300 MHz, the spectrum is not first order since the two CH2 groups and the CH group are severely overlapped and cannot be analyzed by inspection. At 600 MHz, they are fairly well separated and can be analyzed by inspection despite a minor overlap and some distortion. At 300 MHz, the Pople notation is A2B2CX3, which becomes A2G2MX3 at 600 Hz. Note that there is flexibility in choosing letters that are close together and those that are more widely separated. 

For each compound given below (a-o), describe all spin systems (using Pople notation where appropriate), chemically shift equivalent protons, magnetic equivalent protons, enantiotopic protons, and diastereotopic protons. 

Spin systems (collections of interacting nuclei) are often labeled (Pople notation) by assigning a letter from the alphabet to each set of magnetically equivalent nuclei. Nuclei that are close (but not identical) in chemical shift are given letters that are close in the alphabet (e.g., AB). Two nuclei that are chemically equivalent but not magnetically equivalent are assigned the same letter but one letter is primed (e.g., AA ). 

Use Pople notation to identify the types of spin systems that give rise to the spectra shown in Figures 8.20a and b (review problem 8.7). 

Use Pople notation to identify the type of hydro-gen/phosphorus spin system in the structure below ... 

Lipscombhas considered the chemical shifts of the three isomeric icosahedral carboranes, BJ0C2H12 Using the Pople notation it was found that a plot of the corrected shift 5 = o against... 

In the Pople notation, protons that have the same chemical shift are placed in the same set each set is designated by a capital letter. The difference in hertz between two sets is designated Ak The coupling constant J is also determined. The Pople notation depends upon the ratio of Av J. If the ratio is large (arbitrarily greater than about 8), the sets are weakly coupled i.e., they are well separated, and they are designated by well-separated letters of the alphabet (e.g., AM or AX). If... 

Occasionally, it is advantageous to add one further level of complexity to the calculation diffuse functions. Here, heavy atoms are given access to diffuse s- and p-type functions so that their more diffuse orbital regions are considered in calculations. This has relevance for supramolecular chemists interested in anion recognition as diffuse and polarizable orbitals associated with halides are likely to be involved in anion recognition and binding. In Pople notation, these basis sets are denoted by a -I- sign as in 6-311-l-G. ... 

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