(E)-9-(But-2-en-1-yl)-6-chloro-9H-purine

The asymmetric unit of the title compound, C9H9ClN4, contains two molecules. In the crystal, the molecules are ordered in a chain-like fashion along the a axis, and form layers offset relative to the C plane by approximately 30°. This ordering does not, however, appear to be directed by classical hydrogen bonding.The allylic side chains of both independent molecules are disordered, with occupancies of 0.870 (4) and 0.934 (3) for the major components. The disorder components represent two possible spatial orientations of the atoms around the C=C double bond.

The asymmetric unit of the title compound, C 9 H 9 ClN 4 , contains two molecules. In the crystal, the molecules are ordered in a chain-like fashion along the a axis, and form layers offset relative to the C plane by approximately 30 . This ordering does not, however, appear to be directed by classical hydrogen bonding.The allylic side chains of both independent molecules are disordered, with occupancies of 0.870 (4) and 0.934 (3) for the major components. The disorder components represent two possible spatial orientations of the atoms around the C C double bond.

Related literature
For synthetic background and applications, see Kania & Gundersen (2013 We acknowledge the support from the Norwegian Research Council (KOSK II, project 184929 and RENERGI, project 190980) and from the Department of Chemistry, UiO. We also acknowledge Dr David S. Wragg for invaluable assistance with the refinement.

Comment
The title compound is an N-allyl substituted purine intended as a starting material for investigation of the double bond rearragement in N-allylic systems. (E)-9-(but-2-en-1-yl)-6-chloro-9H-purine was recrystallized from a mixture of E/Zisomers in order to obtain the pure E-isomer for the following rearrangement study. The structure and purity of this compound was originally determined by NMR. Further structure elucidation by SXRD supports the conclusions in our previous report (compound 14a, Kania et al., 2013).
The structure of the title compound, C 9 H 9 ClN 4 , has a triclinic P -1 symmetry. The asymmetric unit consists of two molecules of the title compound, with the full content of the unit cell generated by symmetry operations. The molecule has a planar bicyclic motif with an N-allylic chain oriented out of the plane described by the bicyclic main body. During the initial refinement of the structure it became apparent that the N-allylic chain is slightly disordered, with two possible spacial orientations. By using the PART instruction in SHELXL, the two possible orientations of the chain (A and B) were refined individually for the two molecules that form the asymmetric unit (residue 1 and 2). Orientation A is clearly preferred in the solid state, with the minor orientation B present in about 13% and 6.6% abundance for residue 1 and 2 respectively. The limited occupancy of the minor components prompted the use of restraints to achieve satisfactory refinement of the structure. We employed the SADI instruction in SHELXL and restrained the C10, C11B-C13B and C20, C21B-C23B bond distances in the minor components to be the same as the corresponding distances in the major components (C10, C11A-C13A and C20, C21A-C23A). This ensured realistic bond distances in the chains.
Furthermore, C11B-C13B and C21B-C23B were refined isotropically since anisotropic refinement did not give realistic thermal parameters due to the low occupancy of the sites.

Experimental
The title compound was synthesized by the method described in Kania et al. (2013) (compound 14a).

Special details
Experimental. Due to the weak scattering nature of the compound, a large crystal (1.13x0.35x0.22 mm) was used to get satisfactory data for refinement. Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.