| Project/Area Number |
14540465
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Physical chemistry
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| Research Institution | Gunma University |
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Principal Investigator |
TOBITA Seiji Gunma University, Department of Chemistry, Professor, 工学部, 教授 (30164007)
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| Co-Investigator(Kenkyū-buntansha) |
YAMAJI Minoru Gunma University, Department of Chemistry, Associate Professor, 工学部, 助教授 (20220361)
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| Project Period (FY) |
2002 – 2003
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| Project Status |
Completed (Fiscal Year 2003)
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| Budget Amount *help |
¥3,200,000 (Direct Cost: ¥3,200,000)
Fiscal Year 2003: ¥1,300,000 (Direct Cost: ¥1,300,000)
Fiscal Year 2002: ¥1,900,000 (Direct Cost: ¥1,900,000)
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| Keywords | proton transfer / aniline / acid-base equilibrium / fluorescence / radiationless transition / solvent relaxation / isotope effect / water structure / 置換基効果 / 水 |
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| Research Abstract |
Proton dissociation from the lowest excited singlet state of protonated aniline derivatives in aqueous solution was studied by picosecond time-resolved fluorescence measurements. The proton dissociation rate was significantly influenced by introduction of an ortho-alkyl group(s) to aniline as 1.4 x 10^<10>s^<-1> for aniline, 4.1 x 10^9s^<-1> for 2-toluidine and 1.7 x 10^9s^<-1> for 2,6-xylidine. The remarkable decrease of the proton dissociation rate by alkylation was attributed partly to change in exothermicity of the reactions. The activation barrier for the proton-dissociation reaction was increased in the alkylated anilines, suggesting that the hydrophobic effects of the alkyl group on the water structure in the vicinity of the amino group influences the rate of proton transfer to solvent.
Substituent effects on the proton dissociation of protonated aniline derivatives upon femtosecond laser pulse excitation were investigated for m-and p-cyanoanilines and m-and p-methoxyanilines in aqueous solution. The cyano substitution at the meta-position increased the rate significantly (k_<dis> = 3.7 x 10^<11>s^<-1>) compared to aniline (k_<dis> = 1.3 x 10^<10>s^<-1>), while the methoxy substitution reduced the rate remarkably. Either substituent at the para-position showed only slight influences on the rate. The strong dependences of the k_<dis> value on the substituent and the substituted position were reasonably explained on the basis of the free energy change.
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