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Volumn 133, Issue 25, 2011, Pages 9812-9823

Isomerization mechanism in hydrazone-based rotary switches: Lateral shift, rotation, or tautomerization?

Author keywords

[No Author keywords available]

Indexed keywords

ARYLHYDRAZONE; DOUBLE BONDS; E-ISOMERS; FUNCTION ANALYSIS; HYDRAZONES; HYDROGEN BONDED SYSTEMS; KINETIC DATA; LATERAL SHIFTS; MOLECULAR SWITCHES; NATURAL BOND ORBITAL; NEGATIVE ENTROPIES; NON-POLAR; POLARIZED TRANSITION STATE; PROTONATED; RATE CONSTANT K; REVERSIBLE SWITCHING; ROTATION MECHANISM; SINGLE BOND; SOLVENT POLARITY; TAUTOMERIZATIONS; TRANSITION STATE; TRIFLUOROACETIC ACIDS;

EID: 79959498007     PISSN: 00027863     EISSN: 15205126     Source Type: Journal    
DOI: 10.1021/ja200699v     Document Type: Article
Times cited : (171)

References (173)
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    • For some examples of conflicting reports on hydrazone isomerization mechanism, please see ref 25a and
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    • imin=N atoms it is -3.16(10)° for 1- E and -8.23(10)° for 2- E
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    • These types of hydrazones usually adopt planar structures. For other examples, please see: Vickery, B.; Willey, G. R.; Drew, M. G. B. J. Chem. Soc., Perkin Trans. 2 1981, 155-160
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    • The bond length between the aromatic carbon and the hydrazone nitrogen (N2) is 1.401(1) Å for 1- E and 1.400(1) Å for 2- E, and the N(1)-N(2) bond length is 1.321(1) Å for 1- E and 1.326(1) Å for 2- E. The length of the imino double bond (C=N) is 1.305(1) Å for 1- E and 1.313(1) Å for 2- E.
    • The bond length between the aromatic carbon and the hydrazone nitrogen (N2) is 1.401(1) Å for 1- E and 1.400(1) Å for 2- E, and the N(1)-N(2) bond length is 1.321(1) Å for 1- E and 1.326(1) Å for 2- E. The length of the imino double bond (C=N) is 1.305(1) Å for 1- E and 1.313(1) Å for 2- E.
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    • The reason for this is most probably the unfavorable peri interaction in the other conformation (rotamer).
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    • The error in the calculated absolute nuclear magnetic shifts was ∼1 ppm. However, the error in the relative nuclear magnetic shifts was observed to be ∼0.1 ppm.
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    • 3 is used as the base, the fully equilibrated spectrum is generated instantaneously, and this process is not observed.
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    • +.
    • +.
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    • Regardless of the isomerization or the protonation states of the hydrazone-based switches 1 and 2, the main absorption of 2 is constantly 10-20% less intense than that of 1.
    • Regardless of the isomerization or the protonation states of the hydrazone-based switches 1 and 2, the main absorption of 2 is constantly 10-20% less intense than that of 1.
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    • It is noteworthy that, at the beginning of the spectrophotometric titrations of 1- E and 2- E by TFA (Figures S15 and S16 in the SI), unexpected spectral variations were observed. These changes were attributed to the initial protonation of the Z isomer, which has more basic pyridyl nitrogen, as it is not involved in H-bonding as is the case in the E isomer. This observation supports the presence of a mixture of Z and E isomers in solution, in agreement with the NMR data. The E isomers remain by far the predominant species in solution (estimated >95%).
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    • Z→E values were used for the different calculations.
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    • 3CN (see ref 28a) was overestimated because base catalysis was not taken into account.
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    • Given that the accuracy of our computational method is likely to be around ∼1 kcal/mol, we believe that our calculations are not able to distinguish the difference between the barriers of 1 and 2.
    • Given that the accuracy of our computational method is likely to be around ∼1 kcal/mol, we believe that our calculations are not able to distinguish the difference between the barriers of 1 and 2.
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    • E H+→ Z H+. For this reason we have used c = 0 in our calculations.
    • E H+→ Z H+. For this reason we have used c = 0 in our calculations.


* 이 정보는 Elsevier사의 SCOPUS DB에서 KISTI가 분석하여 추출한 것입니다.