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In chemistry, the Z-matrix is a way to represent a system built of atoms.A Z-matrix is also known as an internal coordinate representation.It provides a description of each atom in a molecule in terms of its atomic number, bond length, bond angle, and dihedral angle, the so-called internal coordinates, [1] [2] although it is not always the case that a Z-matrix will give information regarding ...
In stereochemistry, a torsion angle is defined as a particular example of a dihedral angle, describing the geometric relation of two parts of a molecule joined by a chemical bond. [ 4 ] [ 5 ] Every set of three non-colinear atoms of a molecule defines a half-plane.
The position of each atom is determined by the nature of the chemical bonds by which it is connected to its neighboring atoms. The molecular geometry can be described by the positions of these atoms in space, evoking bond lengths of two joined atoms, bond angles of three connected atoms, and torsion angles (dihedral angles) of three consecutive ...
This type of representation clearly illustrates the specific dihedral angle between the proximal and distal atoms. [ 2 ] This projection is named after American chemist Melvin Spencer Newman , who introduced it in 1952 as a partial replacement for Fischer projections , which are unable to represent conformations and thus conformers properly.
If we hold carbon atoms 1, 2, and 3 stationary, with the correct bond lengths and the tetrahedral angle between the two bonds, and then continue by adding carbon atoms 4, 5, and 6 with the correct bond length and the tetrahedral angle, we can vary the three dihedral angles for the sequences (2,3,4), (3,4,5), and (4,5,6).
For each molecule, the three substituents emanating from each carbon–carbon bond are staggered, with each H–C–C–H dihedral angle (and H–C–C–CH 3 dihedral angle in the case of propane) equal to 60° (or approximately equal to 60° in the case of propane). The three eclipsed conformations, in which the dihedral angles are zero, are ...
Because dihedral angle values are circular and 0° is the same as 360°, the edges of the Ramachandran plot "wrap" right-to-left and bottom-to-top. For instance, the small strip of allowed values along the lower-left edge of the plot are a continuation of the large, extended-chain region at upper left.
[12] cis-Azobenzene is nonplanar with a C-N=N-C dihedral angle of 173.5° and an N-N distance of 1.251 Å. [13] The trans isomer is more stable by approximately 50 kJ/mol, and the barrier to isomerization in the ground state is approximately 100 kJ/mol. Azobenzene photoisomerization.