TY - JOUR

T1 - Pseudorotational Landscape of Seven-Membered Rings

T2 - The Most Stable Chair and Twist-Boat Conformers of ε-Caprolactone

AU - Jahn, Michaela K.

AU - Dewald, David A.

AU - Vallejo-Lõpez, Montserrat

AU - Cocinero, Emilio J.

AU - Lesarri, Alberto

AU - Zou, Wenli

AU - Cremer, Dieter

AU - Grabow, Jens Uwe

PY - 2014/10/10

Y1 - 2014/10/10

N2 - The conformational landscape and ring-puckering properties of ε-caprolactone have been analyzed by using microwave spectroscopy and quantum chemical calculations. Two conformers were detected in a supersonic jet expansion, the most stable form being a chair containing the ester group in its rectangular flap. This conformation benefits from reduced CH2 bond eclipsing and angle strain, while π-electron delocalization in the ester group is increased. The derived effective structure of the chair form satisfactorily agrees with the calculated near-equilibrium structure. A twist-boat conformer was also identified (9.4 kJ mol-1 higher in energy at CCSD(T)/aug-cc-pVTZ level), and was located in the boat-twist-boat pseudorotation cycle of the seven-membered ring. Three other low-energy conformers were investigated and characterized in terms of the four puckering coordinates of the seven-membered ring. Potential interconversions in the four-dimensional conformation space are also discussed. Twisting rings: The pseudorotation interconversion pathways of the seven-membered ring of ε-caprolactone have been studied by using microwave spectroscopy and theoretical methods based on Cremer-Pople ring-puckering coordinates. The molecule adopts two preferred chair and twist-boat conformations (see figure).

AB - The conformational landscape and ring-puckering properties of ε-caprolactone have been analyzed by using microwave spectroscopy and quantum chemical calculations. Two conformers were detected in a supersonic jet expansion, the most stable form being a chair containing the ester group in its rectangular flap. This conformation benefits from reduced CH2 bond eclipsing and angle strain, while π-electron delocalization in the ester group is increased. The derived effective structure of the chair form satisfactorily agrees with the calculated near-equilibrium structure. A twist-boat conformer was also identified (9.4 kJ mol-1 higher in energy at CCSD(T)/aug-cc-pVTZ level), and was located in the boat-twist-boat pseudorotation cycle of the seven-membered ring. Three other low-energy conformers were investigated and characterized in terms of the four puckering coordinates of the seven-membered ring. Potential interconversions in the four-dimensional conformation space are also discussed. Twisting rings: The pseudorotation interconversion pathways of the seven-membered ring of ε-caprolactone have been studied by using microwave spectroscopy and theoretical methods based on Cremer-Pople ring-puckering coordinates. The molecule adopts two preferred chair and twist-boat conformations (see figure).

KW - ab initio calculations

KW - conformation analysis

KW - lactones

KW - medium-ring compounds

KW - rotational spectroscopy

UR - http://www.scopus.com/inward/record.url?scp=84946776019&partnerID=8YFLogxK

U2 - 10.1002/chem.201403379

DO - 10.1002/chem.201403379

M3 - Article

AN - SCOPUS:84946776019

VL - 20

SP - 14084

EP - 14089

JO - Chemistry - a European journal

JF - Chemistry - a European journal

SN - 0947-6539

IS - 43

ER -