TY - JOUR
T1 - Sulfur-Bridged pen-Naphthalenes
T2 - Synthesis, Conformational Analysis, and Photoelectron Spectroscopy of the Mono-, Di-, and Trisulfides of 1,8-Dimethylnaphthalene
AU - Guttenberger, Hans G.
AU - Bestmann, Hans J.
AU - Dickert, Franz L.
AU - Jorgensen, Flemming S.
AU - Snyder, James P.
PY - 1981/1/1
Y1 - 1981/1/1
N2 - The sulfur-bridged 1,8-peri-naphthalenes 3H,7H-naphtho[1,8-de]-1,2-dithiepin (8) and 4H,8H-naphtho[1,8-ef]-1,2,3-trithiocin (9) have been prepared. Their variable-temperature 1H NMR spectra reveal the presence of conformations undergoing rapid equilibration. For the disulfide (8) line-shape analysis yields a single interconversion with ∆H* = 9.3 kcal/mol and ∆S* = -1.2 cal/(mol K). Two processes are resolvable for the trisulfide (9), a relatively rapid one with ∆H* = 15.4 kcal/mol and ∆S* = -1.1 cal/(mol K) and a slower exchange with ∆G* = 17.9 kcal/mol. Interpretation of the DNMR data was assisted by molecular mechanics calculations and photoelectron spectroscopic measurements. It is concluded that the disulfide (8) exists as an unsymmetrical twist-boat conformer with an S-S dihedral angle of ca. 40°. On the NMR time scale, racemization occurs via a boat conformation (Cs symmetry) with a predicted barrier of ∆E = 7.5 kcal/mol. The calculations suggest, however, an accompanying but lower energy transformation (∆E = 5.4 kcal/mol) which interconverts superimposable enantiomers by way of a twist transition state of C2 symmetry. For the trisulfide (9) the force field calculations indicate the boat structure to be 0.6 kcal/mol more stable than the chair conformation. Boat-boat interchange is suggested to take place through an intermediate twist form (∆E = 13.6 kcal/mol) and is lower in energy than the corresponding boat-chair equilibration.
AB - The sulfur-bridged 1,8-peri-naphthalenes 3H,7H-naphtho[1,8-de]-1,2-dithiepin (8) and 4H,8H-naphtho[1,8-ef]-1,2,3-trithiocin (9) have been prepared. Their variable-temperature 1H NMR spectra reveal the presence of conformations undergoing rapid equilibration. For the disulfide (8) line-shape analysis yields a single interconversion with ∆H* = 9.3 kcal/mol and ∆S* = -1.2 cal/(mol K). Two processes are resolvable for the trisulfide (9), a relatively rapid one with ∆H* = 15.4 kcal/mol and ∆S* = -1.1 cal/(mol K) and a slower exchange with ∆G* = 17.9 kcal/mol. Interpretation of the DNMR data was assisted by molecular mechanics calculations and photoelectron spectroscopic measurements. It is concluded that the disulfide (8) exists as an unsymmetrical twist-boat conformer with an S-S dihedral angle of ca. 40°. On the NMR time scale, racemization occurs via a boat conformation (Cs symmetry) with a predicted barrier of ∆E = 7.5 kcal/mol. The calculations suggest, however, an accompanying but lower energy transformation (∆E = 5.4 kcal/mol) which interconverts superimposable enantiomers by way of a twist transition state of C2 symmetry. For the trisulfide (9) the force field calculations indicate the boat structure to be 0.6 kcal/mol more stable than the chair conformation. Boat-boat interchange is suggested to take place through an intermediate twist form (∆E = 13.6 kcal/mol) and is lower in energy than the corresponding boat-chair equilibration.
UR - http://www.scopus.com/inward/record.url?scp=0000518768&partnerID=8YFLogxK
U2 - 10.1021/ja00391a029
DO - 10.1021/ja00391a029
M3 - Journal article
AN - SCOPUS:0000518768
SN - 0002-7863
VL - 103
SP - 159
EP - 168
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
IS - 1
ER -