title: Stereochemistry of a spherand-type calixarene.
abstract: The stereochemistry of the spherand-type calixarene 2a is analyzed in terms of the configuration of the three 2,2'-dihydroxybiphenyl subunits (R or S) and the disposition of the methylene groups (crown or twist). X-ray crystallography indicates that the neutral 2a and its mono- or dianion (in form of the salts 2a(-) x C(5)H(5)NH(+) and 2a(2)(-) x 2Et(3)NH(+)) exist essentially in the same conformation (RRS/SSR-twist). This asymmetric RRS/SSR-twist form is the lowest energy conformer according to molecular mechanics calculations. Low-temperature (1)H NMR data indicate the presence of a major conformer of C(1) symmetry, in agreement with a RRS/SSR-twist form. The lowest energy topomerization pathway mutually exchanges two pairs of methylene protons and is ascribed to an enantiomerization process involving rotation around an Ar-Ar bond.
authors.affiliation: Department of Organic Chemistry, The Hebrew University of Jerusalem, Jerusalem, 91904, Israel.
authors.forename: K
authors.initials: K
authors.lastname: Agbaria
authors.forename: S E
authors.initials: SE
authors.lastname: Biali
authors.forename: V
authors.initials: V
authors.lastname: Böhmer
authors.forename: J
authors.initials: J
authors.lastname: Brenn
authors.forename: S
authors.initials: S
authors.lastname: Cohen
authors.forename: M
authors.initials: M
authors.lastname: Frings
authors.forename: F
authors.initials: F
authors.lastname: Grynszpan
authors.forename: J M
authors.initials: JM
authors.lastname: Harrowfield
authors.forename: A N
authors.initials: AN
authors.lastname: Sobolev
authors.forename: I
authors.initials: I
authors.lastname: Thondorf