Propane dihedral angle

Vicinal CH coupling constants Hqh resemble vicinal HH coupling constants in the way that they depend on the cosine of the dihedral angle 9 between the CC bond to the coupled C atom and the C//bond to the coupled proton (cf Fig. 2.16), as illustrated by the Newman projections of the conformers 20a-c of a propane fragment. 

Reduction of Ni11 chloride complexes [NiCl2(L)] (L = various diphosphinomethanes, -ethanes, and -propanes) with, for example, potassium naphthalenide in THF gives the corresponding Ni1 chlorides [NiCl(L)].2368 By treatment of (963) with LiNHAr, a terminal amido complex of Ni1 (964) was prepared (Scheme 13).2369 It contains planar three-coordinate nickel and a planar amido ligand with d(Ni—N) = 1.881(2) A. The P,Ni,P and C,N,H planes are orthogonal with a 91° dihedral angle. 

An interesting Ni(II) complex is the bis(dimethylphosphino)propane complex [Ni(dmpp)i]2 +. As illustrated in Figure 100, it possesses a geometry intermediate between planar and tetrahedral in that the dihedral angle between the two coordinated dmpp ligands is about 44°.154... 

Structural dependences of 4J(F1,F[) in propanic and allylic systems were recently studied by Barfield29 calculating, within the FPT-DFT approach, the FC term of such couplings. In propane Barfield carried out calculations for different values of the dihedral angles about the C3 C2 and C2 C3 bonds and for different values of the C3 C2 C3 internal angle. Using these calculated values he established a four-term trigonometric expression, which was then... 

In aliphatic and cycloaliphatic compounds, vicinal carbon-proton coupling constants 3Jch are related to the dihedral angle 0, as known from the Karplus-Conroy relation for iJ[iH. The Fermi-contact contribution to 3JCH as a function of the dihedral angle 0 calculated for propane [131] is displayed in Fig. 3.15, and the Karplus relation given by eq. (3.17) can be derived ... 

Draw a plot of energy versus dihedral angle for the conformations of propane about one of the C—C bonds. 

How would the energy versus dihedral angle plot for 2-methylpropane (isobutane) differ from that for propane ... 

Fig. 10. 3D plot and contour map for Vhccch in propane, calculated as a function of the dihedral angles ip, and ip3 by DFT/FPT at 30° intervals of the angles. 3D spline interpolations were used to create the graphs, which illustrate how the coupling constant changes sign, depending on the values of, i and, ... 

Figure 18 Torsional potentials in propane as a function of the torsional angle. The torsional angle was arbitrarily chosen as the H —C3 —Cl—C2 dihedral angle (see the inset for notation). Empty squares CH3" H4,H5 interaction. Triangles Me" C3 interaction. Solid line sum of all 1-4 integrated dihedral potentials. Filled squares ab initio points from Ref. (118). The experimental barrier for internal rotation is 3.3 kcal/mol from Ref. (126).

Torsional strain resulting from eclipsed C—H bonds is approximately 4.2 kj (1.0 kcal)/mol, and that for eclipsed C—H and C—CHj bonds is approximately 6.3 kJ (1.5 kcal)/mol. Given this information, sketch a graph of energy versus dihedral angle for propane. 

FIGURE 2.27 A graph of energy versus dihedral angle (0) for propane. 

Fig. 2.9 The propane potential energy surface as the two HCCC dihedrals are varied (calculated by the AMI method, Chapter 6). Bond lengths and angles were not optimized as the dihedrals were varied, so this is not a relaxed PES however, changes in bond lengths and angles from one propane conformation to another are small, and the relaxed PES should be very similar to this one...

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