Phosphorus-hydrogen coupling constants

The conformation of the synthetic putative ligatin receptor has been determined by its phosphorus carbon and phosphorus hydrogen coupling constants [234]. The pseudo-saccharide bond to phosphorus adopts a normal conformation and obeys the exo anomeric effect. The total shape of this pseudo disaccharide is a stretched out conformation. 

In all cases fluorine-fluorine and fluorine-hydrogen coupling constants are indicated in column (4) by two numbers separated by a hyphen [e.g. (1-2) indicates a J(F-F) or J(F-H) between nuclei numbered (1) and (2) in the structural formula in column (2)], or by numbers followed by letters for AB systems [e.g. (2A-2B) indicates a J(F-F) between fluorine nuclei of an AB system numbered (2) in the structural formula in column (2)]. Other couplings are represented by a number for the fluorine (or F) and an element symbol separated by a hyphen, with the higher atomic number nucleus having priority. The element involved in the coupling may be numbered, but the coupled nuclei, other than fluorine, are always denoted by the element symbol followed by the number [e.g. a coupling between phosphorus and fluorine may appear in column (4) as (P-2), (P-FX (Px-2X (Px-FX V(P-FX V(Px-2), or V(Px-FX where x, y, and 2 are int ers ]. The above should be self-evident from the tables. 

First of all we have three problems where the structure is known. Here you are asked to calculate coupling constants between phosphorus and carbon or hydrogen (Problem 36) and relaxation times T for carbon nuclei (Problem 37) and phosphorus nuclei (Problems 38a and 38b). Note that the equation you will require for Tj calculations can be found in Fig. 10 on p. 19... 

In systems derived from PH3 BH3, changes in the coupling constant, /pH, are found which are similar to those seen in compounds derived from PH3, i.e. compounds with phosphorus in coordination number 3. The observation that the alteration does not correspond to that seen for derivatives of PHi suggests that the very weak donor-acceptor bond in PH3 BH3 does not affect the hybridisation of phosphorus, as compared with that in free PH3, as much as might at first be expected. A small increase in the electron withdrawing action by halogen substitution of the hydrogen atoms bonded to boron causes an increase in the s character of the P-H bonds. 

In Jpjj and coupling, the phosphorus and hydrogen atoms are separated by one fj) or two ( J) atoms of the backbone - typically carbon atoms. This arrangement leads to a Karplus-like dependance of the and vicinal Jpjj coupling constants on the dihedral angle 0. 

In going from secondary to primary phosphanides, the expected upheld shift in the phosphorus resonance is observed as primary phosphanes are usually found upheld from the respective secondary phosphanes. Substituting a phenyl group with a hydrogen atom does not only create an upheld shift in the phosphorus resonance, but also introduces asymmetry into the complex (see Fig. 7.11). There are now three stereoisomers observable. They are differentiated by the relative positions of the phenyl and hydrogen substituents on the phosphorus atoms. Each of the three isomers has its characteristic multiplet pattern, with accompanying and Jpp coupling constants. 

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