array(5) {
  ["C"]=>
  float(32)
  ["H"]=>
  float(26)
  ["N"]=>
  float(2)
  ["O"]=>
  float(2)
  ["Ni"]=>
  float(1)
}

• This is an implementation of an Excel spreadsheet calculation which was created by Flack/Shmueli: H. D. Flack and U. Shmueli, Acta Crystallogr. A, 2007, 63, 257–265.
• A Friedif value of 80 or more indicates only few absolute structure determination problems. A Friedif value of 34 or lower indicates difficulties to reach an e.s.d. on the Flack parameter less than 0.1. (see H. D. Flack, Acta Chim. Slov., 2008, 55, 689–691.)
• The quality of an absolute structure determinations is often derived from the Flack parameter x along with its associated e.s.d. u, thus x(u). u < 0.04 is associated with a strong inversion-distinguishing power, 0.04 < u < 0.1 means enantiopure-sufficient inversion-distinguishing power. A reliable absolute structure determination requires u < 0.04 and |x| < 2u. If there is a priori biological, chemical, or physical evidence for true enantiopurity of the compound of interest, 0.04 < u < 0.1 and |x| < 2u is also acceptable. see H. D. Flack and G. Bernardinelli, J. Appl. Cryst., 2000, 33, 1143–1148.

Timo Stein, 2019