Endo ring conformation

Enantiotopic atoms or groups 479 Endergonic reactions 286 Endo ring conformation 212 Endocytosis 13,425-427 Endoderm 23 Endoglucanases 602 Endoglycanases 593, 602 Endonexin SeeAnnexin Endoplasmic reticulum (ER) 10,13,14, 521 cisternae of 14 definition of 14 in micrograph 13 rough 14 smooth 14 Endosomes 13, 426 Endosperm 30... 

It is concluded that one isomer has the methyl group below the basal plane of the boron framework (endo-) with the CF3 group nearly in the plane of the base in an axial (exo-) position and in the other isomer the conformation is the opposite, but no assignment was made. Marynick and Onak 180> have suggested, on the basis of their ring current model for the correlation of chemical shifts in pyramidal boron compounds, that the proton chemical shifts reported for the methyl groups of these two isomers 174> favor assignment of the endo-methyl conformation to isomer A. 

An X-ray structural analysis of SegfAlCUlg revealed a bicyclic cation structure whose characteristic feature is an endo-exo conformation of the eight-membered ring. The molecular symmetry is approximately C8 (see Fig. 9). 

No structural data are available for S g. The crystal structure of 8g(AsFg)2 has been determined (67) it contains the 8g ion which has the structure shown in Fig. 3. It consists of a folded ring with approximately Cg symmetry and has an endo-exo conformation. The average bond distance around the ring is 2.04 A, which is identical with that in the 83 molecule (73, 74). The three cross-ring distances, as determined in the two crystallographically different 8g rings, are 84-83 [2.942(10),... 

In addition, Sg ring conformations of lower symmetry than 04a are hkely candidates in liquid sulfur. For example, the exo-endo isomer 3 (Fig. 4) is by only AG°298=27.8 kJ mol" less stable than the ground state conformation and therefore its relative concentration in liquid sulfur at the boiling point will be also ca. 1% of all Sg species [109]. 

Fig. 9.12. Scattergram of the scores on the first two factors from a principal component analysis of the torsion angles of 181 furanose rings. The two factors include essentially 100% of the variance of the ring torsion angles. The numbers show the position of some selected ring conformations. 1 envelope (e) with mirror plane through C(2 ) endo 2 e C(3 ) endo 3 e C(3 ) exo 4 e C(2 ) exo 5 twist with Ci axis through C(T) 6 e 0(T) endo...

Other than B-form DNA, there are other forms of DNA that are more distorted from Watson and Crick ideality. These include A-form, C-form, D-form and T-form DNA. Of these, A-form DNA is the most similar to B-form DNA (Figure 1.73). The only major difference is that the 2 -deoxy-/3-D-ribofuranose rings of A-form DNA exist in an alternative C -endo twist conformation (Figures 1.71 and 1.73). Consequently, the helix diameter is wider and there are 11 base pair residues per turn (Table 1.2). A-form DNA also possesses shallow major and minor grooves. Z-form DNA, by contrast, is radically different from B-form... 

DNA (Table 1.2) (Figure 1.74). The helbc sense of Z-form DNA is now left handed and the backbones of the two poly deoxynucleotide chains map out a zigzag spiral path. This results from the tendency of deoxyguanosine nucleotide residues to distort so that their 2 -deoxy-/3-D-ribofuranose rings adopt a C -endo instead of C -endo twist conformation (Figure 1.71). However, in addition, the guanine bases move to a syn conformation (positioned over the top of their attached furanose rings), instead of the more usual anti conformation... 

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