N 4 1 rule

More complicated splitting patterns conform to an extension of the n + 1 rule and will be discussed in Section 13 11... 

It turns out that fully filled or half-filled subshells have added stability compared with subshells having some other numbers of electrons. One effect of this added stability is the fact that some elements do not follow the n +1 rule exactly. For example, copper would be expected to have a configuration... 

To get the electron configuration of ions, a new rule is followed. We first write the electron configuration of the neutral atom. Then, for positive ions, we remove the electrons in the subshell with highest principal quantum number first. Note that these electrons might not have been added last, because of the n + / rule. Nevertheless, the electrons from the shell with highest principal quantum number are removed first. For negative ions, we add electrons to the shell of highest principal quantum number. (That shell has the electrons added last by the n +1 rule.)... 

A given peak will be split into a number of peaks equal to the number of equivalent hydrogens on the adjacent carbons plus 1 (the n + 1 rule). This represents a clue about the structure that can help lead to identification of the compound. 

The additional detail provided by a high resolution spectrum allows more information to be determined about the structure of the compound. Analysing the multiplets allows the neighbouring proton environment to be identified. This can be done using the n + 1 rule, where n is the number of carbon atoms attached to the next-door carbon atom and n + 1 is the number of peaks that will be seen in the cluster. 

One particularly interesting category of metallocarborane is that in which a single metal atom is shared between two polyhedra that have a vertex in eommon. In effect, the metal is sandwiched between two nido-carborane residues. Examples are shown in Fig. 17. For such commo compounds, the metal can be assumed to contribute three AO s to the skeletal bonding of each polyhedron, when the (n + 1) rule for closo clusters is found to be obeyed. For example, the isoelectronic... 

Coupling follows the n + 1 rule. According to this rule, a peak splits into n + 1 peaks due to neighboring hydrogen atoms, where n is the number of equivalent hydrogen atoms. The amount of splitting is expressed by the coupling constant (J). 

The interaction of an unpaired electron with three equivalent protons as in CHS radical gives four equally spaced lines according to (n + 1) rule. 

A French group of writers and mathematicians called the Oulipo still discuss and create literary works involving constrained writing, which provides them with a means of triggering ideas, inspiration, and mind expansion. The Oulipo (Ouvrior de Utterature P tentielle) have experimented with such constraints as the N+1 rule in which every noun in a story is replaced with the word that falls 7 words ahead of it in the dictionary. Thus, Call me Ishmael from might become Call me... 

The n + 1 rule should be amended to read When a proton H is coupled to Hfo, Hc, H(i, etc., and Jab Jac, Jad, etc., the original signal for Ha is split into n + 1 peaks by n H, protons, each of these lines is further split into n + 1 peaks by n Hc protons, and each of these into n + 1 lines by n H(i protons, and so on. Bear in mind that because of overlapping peaks, the number of lines actually observed can be less than that expected on the basis of the splitting rule. 

If a proton or set of protons is not coupled equally to neighboring protons, then die n + 1 rule is not adequate to describe the multiplicity of die absorption. Instead one observes multiplets of multiplets as the splitting pattern (e.g., doublet of doublets or triplet of doublets). The multiplicity can be understood by carrying out sequential splitting diagrams. For example, consider a proton II/, split by two neighboring vicinal protons II and Hc by Jab = 2 Hz and Jbc = 1 Hz. This is... 

Know the meaning of NMR, applied magnetic field, spin state, chemical shift, 5 value, TMS (tetramethylsilane), peak area, spin-spin coupling, n+ 1 rule, singlet, doublet, triplet, quartet, MRI. 

If immunogenicity studies demonstrate that a similar immune response is obtained at intervals shorter than the proposed clinical dosing interval (e.g., 4-6 weeks), then a truncated dosing interval (2-3 weeks) can be used in the repeat dose safety studies. The FDA recommends that one more dose than the clinical dosing regimen (N) be used in animal studies. This is termed the N + 1 rule [61].The number of animals used per group should be sufficient to detect... 

The preceding analysis for the splitting of 1,1,2-tribromoethane can be extended to more complicated systems. In general, the multiplicity (number of peaks) of an NMR signal is given by the N +1 rule ... 

This result, shown in Figure 9.14a, is exactly the two doublets we would have expected from the first-order (n +1) rule. 

---