The crystal structures of
β
gutta-percha, rubber and polychloroprene have been determined by interpretation of X-ray diffraction photographs.
β
Gutta-percha (—CH
2
—C(CH
3
)=CH—CH
2
—)n is orthorhombic, with axial lengths a
0
= 7.78 A,
b
0
= 11.78 A,
c
0
= 4.72 A. Four long-chain molecules pass through this cell parallel to the
c
axis. The space group is
P
2
1
2
1
2
1
, and the co-ordinates of the five carbon atoms of one structural unit are: (CH
2
) 0.926 (C) 0.000 (CH) 0.000 (CH
2
) 0.074 (CH
3
) 0.970 0.110 0.146 0.074 0.110 0.277 0.676 0.960 0.177 0.462 0.980 The molecules are asymmetric; all the molecules passing through any one crystal are identical—either left-handed or right-handed, not mixed. The carbon chain is a non-planar zigzag; each chain unit C—C=C—C is planar, and has the
trans
configuration, but the connecting links (CH
2
—CH
2
) lie in a different plane; the plane —C—C—C = makes an angle of 115° with plane —C—C=C—. a Gutta-percha molecules probably also have the
trans
double-bond configuration, and differ from
β
molecules only in the positions of the CH
2
—CH
2
bonds; the chain form is thus different from that of
β
molecules. Crystalline rubber (also (—CH
2
— C(CH
3
)=CH — CH
2
— )
n
) is monoclinic, and has
a
0
= 12.46 A,
b
0
= 8.89 A,
c
0
= 8.10 A,
β
= 92°. Four long-chain molecules pass through this cell parallel to the
c
axis. The space group is
P
2
1
/
a
and the co-ordinates of the ten carbon atoms of one structural chain unit are (CH
2
) 0.753 (C) 0.854 (CH) 0.845 (CH
2
) 0.745 (CH
3
) 0.968 0.899 0.865 0.905 0.959 0.876 0.802 0.703 0.542 0.457 0.773 (CH
2
) 0.744 (C) 0.644 (CH) 0.659 (CH
2
) 0.757 (CH
3
) 0.532 0.834 0.874 0.905 0.834 0.828 0.326 0.215 0.052 0.975 0.268 The molecules are asymmetric; two of the molecules passing through the unit cell are left-handed and two right-handed. The chain carbon atoms of any one molecule form a non-planar zigzag, in which the double-bond units C— C=C— C have the
cis
configuration. The two isoprene units C —C—C=C —C— which make up the structural unit are not identical in configuration; the distortion appears to be due to intermolecular forces. The structure of crystalline polychloroprene (—CH
2
—CCl=CH—CH
2
— )
n
is completely analogous to that of (i gutta-percha. The cell is orthorhombic, with
a
0
= 8.84 A,
b
0
= 10.24 A,
c
0
= 4.79 A. The co-ordinates of carbon and chlorine atoms are (CH
2
) 0.077 (C) 0.033 (CH) 0.008 (CH
2
) 0.970 Cl 0.167 0.054 0.115 0.034 0.099 0.243 0.278 0.000 0.787 0.509 0.000
Total synthesis of verucopeptin, an inhibitor of hypoxia-inducible factor 1 (HIF-1)