  Amongst the derivatives of 4-biphenylcarboxylic acid and amino acid esters,
the crystal structure of 4-biphenylcarboxy-(L)-phenylalaninate is unusual owing
to its monoclinic symmetry within a pseudo-orthorhombic lattice. The distortion
is described by disparate rotational property around the chiral centers
($\varphi_{\mathrm{chiral}}$ $\simeq$ -129 degrees and 58 degrees) of the two
molecules in the asymmetric unit. Each of these molecules comprise of planar
biphenyl moieties ($\varphi_{\mathrm{biphenyl}}$ = 0 degrees). Using
temperature dependent single crystal X-ray diffraction experiments we show that
the compound undergoes a phase transition below $T$ $\sim$ 124 K that is
characterized by a commensurate modulation wave vector, $\mathbf{q}$ =
$\delta(101)$, $\delta$ = $\frac{1}{2}$. The (3+1) dimensional modulated
structure at $T$ = 100 K suggests that the phase transition drives the biphenyl
moieties towards non coplanar conformations with significant variation of
internal torsion ($\varphi^{\mathrm{max}}_{\mathrm{biphenyl}}$ $\leq$ $20$
degrees). These intramolecular rotations lead to dimerization of the molecular
stacks that are described predominantly by intermolecular tilts and small
variations in intermolecular distances. Atypical of modulated structures and
superstructures of biphenyl and other polyphenyls, the rotations of individual
molecules are asymmetric ($\Delta$$\varphi_{\mathrm{biphenyl}}$ $\approx$ 5
degrees) while $\varphi_{\mathrm{biphenyl}}$ of one independent molecule is two
to four times larger than the other. Crystal-chemical analysis and phase
relations in superspace suggest multiple competing factors involving
intramolecular steric factors, intermolecular H--C${\cdot}{\cdot}{\cdot}$C--H
contacts and weak C--H${\cdot}{\cdot}{\cdot}$O hydrogen bonds that govern the
distinctively unequal torsional property of the molecules.
