3-[1-(4-Bromophenyl)ethoxy]-2,2,5-trimethyl-4-phenyl-3-azahexane

The title compound, C22H30BrNO, is an alkoxyamine compound, an effective initiator in nitroxide-mediated free radical polymerization. It was prepared as a mixture of two diasteromers; the crystal for the X-ray analysis showed one of these as a pair of R,S and S,R enantiomers. The tert-butyl and isopropyl groups are in an almost anti conformation in the crystal [C—N—C—C torsion angle = −168.8 (1)°], and the methyl group of the ethoxy group is in an approximate anti relationship to the tert-butyl group. The dihedral angle between the phenyl and benzene rings is 33.12 (7)°. The Br atom is disordered over two positions, with occupancies of 0.9139 (16) and 0.0861 (16). In the crystal, weak C—H⋯Br contacts link the molecules into chains along [-110].

The title compound, C 22 H 30 BrNO, is an alkoxyamine compound, an effective initiator in nitroxide-mediated free radical polymerization. It was prepared as a mixture of two diasteromers; the crystal for the X-ray analysis showed one of these as a pair of R,S and S,R enantiomers. The tert-butyl and isopropyl groups are in an almost anti conformation in the crystal [C-N-C-C torsion angle = À168.8 (1) ], and the methyl group of the ethoxy group is in an approximate anti relationship to the tert-butyl group. The dihedral angle between the phenyl and benzene rings is 33.12 (7) . The Br atom is disordered over two positions, with occupancies of 0.9139 (16) and 0.0861 (16). In the crystal, weak C-HÁ Á ÁBr contacts link the molecules into chains along [110].

Comment
Nitroxide-mediated radical polymerization (NMRP) has been widely used for polymer and block copolymer synthesis, with controlled molecular weight, polydispersity, and end group functionality, and with relatively mild conditions (Benoit et al., 1999;Wetter et al., 2004). In NMRP, an alkoxyamine is used to initiate and mediate polymerization. The C-O bond of an alkoxyamine is stable to normal purification and handling procedures as well as variety of reaction conditions (Rodlert et al., 2000). However, under appropriate conditions, homolysis of the C-O bond occurs, giving a (relatively stable) nitroxide radical and carbon radical which can initiate radical polymerization. The nitroxides are kinetically persistent radicals, and act as reversible traps for the less stable radical intermediates in the polymerization (Nilsen & Braslau, 2006).
The bromine atom was disordered over two positions with occupancies of 0.9139 (16) and 0.0961 (16). The central N is pyramidal and all the bond lengths and angles are in the normal ranges (Allen et al., 1987). There are weak C-H···Br intermolecular contacts which link the molecules into chains in the [-1 1 0] direction.

Refinement
Carbon-bonded hydrogen atoms were included in idealized positions and set to ride on the parent atoms. The bromine atom was disordered over two positions with occupancies of 0.9139 (16) and 0.0961 (16).

Figure 1
Structural diagram of the title compound. Atomic displacement parameters are at the 30% probability level.

Special details
Experimental. CrysAlisPro (Agilent, 2012) Analytical numeric absorption correction using a multifaceted crystal model based on expressions derived by R.C. Clark & J.S. Reid. (Clark & Reid, 1995) 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.