Simultaneous measurement of optical rotation dispersion and absorption spectra for chiral substances

Chirality ◽  
2020 ◽  
Vol 32 (8) ◽  
pp. 1072-1079
Author(s):  
Xing Liu ◽  
Jinlong Yang ◽  
Zhihao Geng ◽  
Hongzhi Jia
Keyword(s):  
Absorption Spectra ◽  
Simultaneous Measurement ◽  
Optical Rotation ◽  
Rotation Dispersion

Rubescins F–H, new vilasinin-type limonoids from the leaves of Trichilia rubescens (Meliaceae)

2019 ◽  
Vol 74 (7-8) ◽  
pp. 175-182
Author(s):  
Armelle Tontsa Tsamo ◽  
Julio Issah Mawouma Pagna ◽  
Pamela Kemda Nangmo ◽  
Pierre Mkounga ◽  
Hartmut Laatsch ◽  
...  
Keyword(s):  
Ab Initio ◽  
Methylene Chloride ◽  
High Resolution Mass Spectrometry ◽  
Optical Rotation ◽  
Cyclopropane Ring ◽  
Dispersion Data ◽  
Rotation Dispersion ◽  
Oxetane Ring ◽  
Related Compounds ◽  
Potential Precursor

Abstract Three new limonoids, designated as rubescins F (1), G (2), and H (3), together with two known compounds of this type, TS1 (4) and trichirubine A (5), were isolated from methylene chloride/methanol extracts of Trichilia rubescens leaves. The structures of these compounds were elucidated based on 1D and 2D nuclear magnetic resonance (NMR) analysis and complemented by electrospray ionization high-resolution mass spectrometry results and by comparison to data of related compounds described in the literature and ab initio calculations. Rubescin F (1) is the first limonoid from Trichilia spp. with an oxetane ring between C-7 and C-14, which seems to be formed by the isomerization of TS1 (4). The γ-hydroxybutenolide rubescin G (2) is a potential precursor of trichirubine A (5), whereas rubescin H (3) is the first example of a triterpenoid with a single bond between C-7/C-14, forming a cyclopropane ring. The absolute configuration of these limonoids was derived from biosynthetic considerations and ab initio calculations of NMR and optical rotation dispersion data.

Correlation Between Optical Activity and the Helical Molecular Orbitals of Allene and Cumulenes

2020 ◽  
Author(s):  
Marc Hamilton Garner ◽  
Clemence Corminboeuf
Keyword(s):  
Electronic Structure ◽  
Optical Activity ◽  
Optical Rotation ◽  
Molecular Orbitals ◽  
Optically Active ◽  
Electronic Transitions ◽  
Frontier Molecular Orbitals ◽  
Chiral Molecules ◽  
Axial Chirality ◽  
Rotation Dispersion

<div><div><div><p>Helical frontier molecular orbitals (MOs) appear in disubstituted allenes and even-n cumulenes. Chiral molecules are optically active, but while these molecules are single-handed chiral, π-orbitals of both helicities are present. Here we computationally examine whether the optical activity of chiral cumulenes is controlled by the axial chirality or the helicity of the electronic structure. We exploit hyperconjugation with alkyl, silaalkyl, and germaalkyl substituents to adjust the MO helicity without altering the axial chirality. For the same axial chirality, we observe an inversion of the helical MOs contribution to the electronic transitions and a change of sign in the electronic circular dichroism and optical rotation dispersion spectra. While the magnitude of the chiroptical response also increases, it is similar to that of chiral cumulenes without helical π-orbitals. Overall, Helical π-orbitals correlate with the big chiroptical response in cumulenes, but are not a prerequisite for it.</p></div></div></div>

Correlation Between Optical Activity and the Helical Molecular Orbitals of Allene and Cumulenes

2020 ◽  
Author(s):  
Marc Hamilton Garner ◽  
Clemence Corminboeuf
Keyword(s):  
Electronic Structure ◽  
Optical Activity ◽  
Optical Rotation ◽  
Molecular Orbitals ◽  
Optically Active ◽  
Electronic Transitions ◽  
Frontier Molecular Orbitals ◽  
Chiral Molecules ◽  
Axial Chirality ◽  
Rotation Dispersion

<div><div><div><p>Helical frontier molecular orbitals (MOs) appear in disubstituted allenes and even-n cumulenes. Chiral molecules are optically active, but while these molecules are single-handed chiral, π-orbitals of both helicities are present. Here we computationally examine whether the optical activity of chiral cumulenes is controlled by the axial chirality or the helicity of the electronic structure. We exploit hyperconjugation with alkyl, silaalkyl, and germaalkyl substituents to adjust the MO helicity without altering the axial chirality. For the same axial chirality, we observe an inversion of the helical MOs contribution to the electronic transitions and a change of sign in the electronic circular dichroism and optical rotation dispersion spectra. While the magnitude of the chiroptical response also increases, it is similar to that of chiral cumulenes without helical π-orbitals. Overall, Helical π-orbitals correlate with the big chiroptical response in cumulenes, but are not a prerequisite for it.</p></div></div></div>

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