The rigidity of the tert-butyl group (TBG) as a substituent in aromatic hydrocarbons is investigated, with a modified Hirshfeld test of anisotropic displacement parameters (ADPs) as a primary criterion. Four new structures are analyzed, along with low-temperature studies of a previously published crowded supermesityl dimer; three of the five structures meet the primary test. Most of the TBGs meet the Hirshfeld test at 100 K, and the ADPs are improved by omitting low-order data in the final refinement. The three most precise structures yield a wide variation in libration amplitudes (and in estimated rotation barriers) for 13 unique TBGs. A similar range of values is found in analyses of structures in the Cambridge Crystallographic Database. The libration amplitudes are calculated with the program THMA14C, with each TBG as an attached rigid group (ARG). Packing analysis suggests that large ADPs, especially for some individual TBG methyl groups, correspond to voids in the crystal. Published barriers to TBG reorientation, determined by solid-state NMR spin-lattice relaxation methods, for six related crystalline compounds are compared with barriers calculated from their crystal structure data.
机构:
Banaras Hindu Univ, Inst Med Sci, Dept Med Chem, Varanasi 221005, Uttar Pradesh, IndiaBanaras Hindu Univ, Inst Med Sci, Dept Med Chem, Varanasi 221005, Uttar Pradesh, India
Kant, Rama
Agarwal, Alka
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Banaras Hindu Univ, Inst Med Sci, Dept Med Chem, Varanasi 221005, Uttar Pradesh, IndiaBanaras Hindu Univ, Inst Med Sci, Dept Med Chem, Varanasi 221005, Uttar Pradesh, India
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Chonbuk Natl Univ, Med Sch & Hosp, Mol Imaging & Therapeut Med Res Ctr, Dept Nucl Med, Jeonju 54907, South Korea
Chonbuk Natl Univ, Chonbuk Natl Univ Hosp, Biomed Res Inst, Res Inst Clin Med, Jeonju 54907, South KoreaChonbuk Natl Univ, Med Sch & Hosp, Mol Imaging & Therapeut Med Res Ctr, Dept Nucl Med, Jeonju 54907, South Korea
Minh Thanh La
Kim, Hee-Kwon
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Chonbuk Natl Univ, Med Sch & Hosp, Mol Imaging & Therapeut Med Res Ctr, Dept Nucl Med, Jeonju 54907, South Korea
Chonbuk Natl Univ, Chonbuk Natl Univ Hosp, Biomed Res Inst, Res Inst Clin Med, Jeonju 54907, South KoreaChonbuk Natl Univ, Med Sch & Hosp, Mol Imaging & Therapeut Med Res Ctr, Dept Nucl Med, Jeonju 54907, South Korea
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Taif Univ, Fac Sci, Dept Chem, Hawiya 888, Saudi Arabia
Kajr El Sheikh Univ, Fac Sci, Dept Chem, Kafr Al Sheikh 33516, EgyptTaif Univ, Fac Sci, Dept Chem, Hawiya 888, Saudi Arabia
Ibrahim, Mohamed M.
Mersal, Gaber A. M.
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Taif Univ, Fac Sci, Dept Chem, Hawiya 888, Saudi Arabia
South Valley Univ, Fac Sci, Dept Chem, Qena, EgyptTaif Univ, Fac Sci, Dept Chem, Hawiya 888, Saudi Arabia
Mersal, Gaber A. M.
El-Shafai, Nagi
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Kajr El Sheikh Univ, Fac Sci, Dept Chem, Kafr Al Sheikh 33516, EgyptTaif Univ, Fac Sci, Dept Chem, Hawiya 888, Saudi Arabia
El-Shafai, Nagi
Youssef, Mohamed M.
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Taif Univ, Fac Sci, Dept Chem, Hawiya 888, Saudi Arabia
Cairo Univ, Fac Sci, Dept Chem, Cairo, EgyptTaif Univ, Fac Sci, Dept Chem, Hawiya 888, Saudi Arabia
Youssef, Mohamed M.
Shokry, Hanaa
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Kajr El Sheikh Univ, Fac Sci, Dept Chem, Kafr Al Sheikh 33516, EgyptTaif Univ, Fac Sci, Dept Chem, Hawiya 888, Saudi Arabia