Magnetic Anisotropy of the C-C Single Bond
Abstract
Anisotropic effects are broadly used in NMR spectroscopy for structure elucidation. With the development of computational methods it has become possible to quantify the effects and obtain further insight into their origin. Some classical interpretations have been questioned. Herein, we show that the classical "anisotropy cone" representing the anisotropic effect of the C-C single bond should be revised: deshielding at its side and shielding along its end are observed. Consequently, methyl, methylene, and methyne hydrogen atoms are not de-shielded by C-C bonds as is conventionally explained in NMR spectroscopy textbooks. They are just less shielded than by the C-H bonds attached at the same carbon. In addition, this anisotropic effect is dependent on the environment and care should be taken when drawing conclusions based on it. For example, it differs for the staggered and eclipsed conformations of ethane in HCCH planes, as well as for cyclohexane. In fact, it is not the anisotropy of t...he C2-C3/C5-C6 bonds that determines the chemical shift difference of axial and equatorial protons of a rigid cyclohexane ring, but magnetic contributions from all bonds.
Keywords:
anisotropic effects / C-C bond / cyclohexane / density functional calculations / NMR spectroscopySource:
Chemistry-A European Journal, 2013, 19, 13, 4249-4254Publisher:
- Wiley-V C H Verlag Gmbh, Weinheim
Funding / projects:
DOI: 10.1002/chem.201204267
ISSN: 0947-6539
PubMed: 23400889
WoS: 000316623200020
Scopus: 2-s2.0-84875150144
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IHTMTY - JOUR AU - Baranac-Stojanović, Marija AU - Stojanović, Milovan PY - 2013 UR - https://cer.ihtm.bg.ac.rs/handle/123456789/1347 AB - Anisotropic effects are broadly used in NMR spectroscopy for structure elucidation. With the development of computational methods it has become possible to quantify the effects and obtain further insight into their origin. Some classical interpretations have been questioned. Herein, we show that the classical "anisotropy cone" representing the anisotropic effect of the C-C single bond should be revised: deshielding at its side and shielding along its end are observed. Consequently, methyl, methylene, and methyne hydrogen atoms are not de-shielded by C-C bonds as is conventionally explained in NMR spectroscopy textbooks. They are just less shielded than by the C-H bonds attached at the same carbon. In addition, this anisotropic effect is dependent on the environment and care should be taken when drawing conclusions based on it. For example, it differs for the staggered and eclipsed conformations of ethane in HCCH planes, as well as for cyclohexane. In fact, it is not the anisotropy of the C2-C3/C5-C6 bonds that determines the chemical shift difference of axial and equatorial protons of a rigid cyclohexane ring, but magnetic contributions from all bonds. PB - Wiley-V C H Verlag Gmbh, Weinheim T2 - Chemistry-A European Journal T1 - Magnetic Anisotropy of the C-C Single Bond VL - 19 IS - 13 SP - 4249 EP - 4254 DO - 10.1002/chem.201204267 ER -
@article{ author = "Baranac-Stojanović, Marija and Stojanović, Milovan", year = "2013", abstract = "Anisotropic effects are broadly used in NMR spectroscopy for structure elucidation. With the development of computational methods it has become possible to quantify the effects and obtain further insight into their origin. Some classical interpretations have been questioned. Herein, we show that the classical "anisotropy cone" representing the anisotropic effect of the C-C single bond should be revised: deshielding at its side and shielding along its end are observed. Consequently, methyl, methylene, and methyne hydrogen atoms are not de-shielded by C-C bonds as is conventionally explained in NMR spectroscopy textbooks. They are just less shielded than by the C-H bonds attached at the same carbon. In addition, this anisotropic effect is dependent on the environment and care should be taken when drawing conclusions based on it. For example, it differs for the staggered and eclipsed conformations of ethane in HCCH planes, as well as for cyclohexane. In fact, it is not the anisotropy of the C2-C3/C5-C6 bonds that determines the chemical shift difference of axial and equatorial protons of a rigid cyclohexane ring, but magnetic contributions from all bonds.", publisher = "Wiley-V C H Verlag Gmbh, Weinheim", journal = "Chemistry-A European Journal", title = "Magnetic Anisotropy of the C-C Single Bond", volume = "19", number = "13", pages = "4249-4254", doi = "10.1002/chem.201204267" }
Baranac-Stojanović, M.,& Stojanović, M.. (2013). Magnetic Anisotropy of the C-C Single Bond. in Chemistry-A European Journal Wiley-V C H Verlag Gmbh, Weinheim., 19(13), 4249-4254. https://doi.org/10.1002/chem.201204267
Baranac-Stojanović M, Stojanović M. Magnetic Anisotropy of the C-C Single Bond. in Chemistry-A European Journal. 2013;19(13):4249-4254. doi:10.1002/chem.201204267 .
Baranac-Stojanović, Marija, Stojanović, Milovan, "Magnetic Anisotropy of the C-C Single Bond" in Chemistry-A European Journal, 19, no. 13 (2013):4249-4254, https://doi.org/10.1002/chem.201204267 . .