Dissociation

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1 - Quantum mechanics investigation of acid dissociation constant of carboxylic acids in aqueous solution
M. Khaleghian Gh. R. Ghashami

According to the Bronsted definition, any compound which has a hydrogen atom is an acid, since itmay be lost as a proton. A thermodynamical cycle is proposed to calculate absolute pKa values forBronsted acids in aqueous solution. The equilibrium of dissociation of a Bro چکیده کامل

According to the Bronsted definition, any compound which has a hydrogen atom is an acid, since itmay be lost as a proton. A thermodynamical cycle is proposed to calculate absolute pKa values forBronsted acids in aqueous solution. The equilibrium of dissociation of a Bronsted acid depends onthe interaction of the acid and its conjugate base with solvent molecules. There fore the pKa valuedepends on the solvent medium. The polarizable continuum model (PCM) was used to describe thesolvent, and absolute pKa values were computed for different compounds: HCOOH, CH3COOH,C6H5COOH, FCH2COOH and CH3CH2COOH. The model of furnishes pKa values was in goodagreement with the experimental results for some classes of compounds. The quantum Mechanics(QM) calculations were carried out with the GAUSSIAN 98 program based on HF/6-31+G** level. پرونده مقاله

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2 - Protonation Constants of Valin in Different Aqueous Solutions of Dimethylsulfoxide
Masumeh Jabbari Ali Shamel Farrokh Ghari

The protonation constants of valin (K1 and K2) was determined in binary mixtures of water with dimethylsulfoxide containing (0, 10, 20, 30, 40, and 50) % (v/v) using a combination of potentiometric method at 25 °C and constant ionic strength (0.1mol ·dm-3 sod چکیده کامل

The protonation constants of valin (K1 and K2) was determined in binary mixtures of water with dimethylsulfoxide containing (0, 10, 20, 30, 40, and 50) % (v/v) using a combination of potentiometric method at 25 °C and constant ionic strength (0.1mol ·dm-3 sodium perchlorate). The protonation constants were analyzed using the normalized polarityparameter (ETN) and Kamlet, Abboud, and Taft (KAT) parameters. A very good linear correlation of log K versus the normalized polarity parameter was obtained. Dual-parameter correlation of log K versus π*(dipolarity/polarizability) and R (hydrogen-bond donor acidity) as well as π* and (hydrogen-bond acceptor basicity) also gives good results in various aqueous organic solvent mixtures. Finally, the results are discussed in terms of the effect of the solvent on the protonation constants. پرونده مقاله

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3 - Determination of the acid dissociation constants of the p-sulphonato-calix[4]arene
Monireh Hajmalek Mohammad Sajjad Khalili Karim Zare Omid Zabihi

10.22034/jna.2014.01.007

The acid dissociation constants of the hydroxyl groups in 25, 26, 27, 28-tetrahydroxy-5, 11, 17, 23-tetrasulphonic-calix[4]arene (SC4) were determined at 25οC by a combination of potentiometric and spectrophotometric titration method. The first and second acid d چکیده کامل

The acid dissociation constants of the hydroxyl groups in 25, 26, 27, 28-tetrahydroxy-5, 11, 17, 23-tetrasulphonic-calix[4]arene (SC4) were determined at 25οC by a combination of potentiometric and spectrophotometric titration method. The first and second acid dissociation constants (pKa1, pKa2) were found to be 3.19 and 12.1, which demonstrated pKa shift due to intramolecular hydrogen bonding interactions among hydroxyl groups in SC4. پرونده مقاله

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4 - Surface modification of γ-alumina by NaNO2, NaNO3, HNO2, HNO3 and H2SO4: A DFT-D approach
Mehdi Zamani Hossein A. Dabbagh

In this study, the dissociative adsorption of NaNO2, NaNO3, HNO2, HNO3 and H2SO4 over (1 1 0) surface of γ-alumina non-spinel model were investigated through the dispersion corrected density functional theory (DFT-D) at PBE-D/DNP level of calculation. It was found چکیده کامل

In this study, the dissociative adsorption of NaNO2, NaNO3, HNO2, HNO3 and H2SO4 over (1 1 0) surface of γ-alumina non-spinel model were investigated through the dispersion corrected density functional theory (DFT-D) at PBE-D/DNP level of calculation. It was found that all of the species are dissociated to their ionic forms after adsorption and relaxation over the surface, i.e. Na+NO2−, Na+NO3−, H+NO2−, H+NO3−, H+HSO4− and 2H+SO42−. The Lewis acidity of alumina surface by addition of HNO2, HNO3 and H2SO4 is increased, while in the presence of NaNO2 and NaNO3, the acidity of catalyst is decreased. Theoretical calculations predict stronger dissociative adsorption of H2SO4 over the surface in compared to other compounds. The HNO2 and HNO3 mineral acids are better adsorbed over the surface than NaNO2 and NaNO3 salts. The better adsorption of nitrites than nitrates is due to the stronger electrostatic attractions. The order of NaNO3 < NaNO2 < HNO3 < HNO2 < H2SO4 for the dissociative adsorption energy of the title compounds is predicted. پرونده مقاله

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5 - بررسی جداسازی پردازش اطلاعات در حافظة عملی و کلامی
رضا کرمی نوری اولا - بریت برامدال لارس گوران نیلسون

در مطالعه حاضر، از روش جداسازی پردازش اطلاعات (PDP) برای دو هدف استفاده شده است: 1. تا سهم پردازشهای خودکار و کنترل شده در تکلیف اجرای عمل (SPT) و تکلیف کلامی (VT) بطور جداگانه انداه گیری شود؛ 2. مشخص شود که آیا دو تکلیف SPT و VT در ارتباط با اندازه پردازش خودکار با هم چکیده کامل

در مطالعه حاضر، از روش جداسازی پردازش اطلاعات (PDP) برای دو هدف استفاده شده است: 1. تا سهم پردازشهای خودکار و کنترل شده در تکلیف اجرای عمل (SPT) و تکلیف کلامی (VT) بطور جداگانه انداه گیری شود؛ 2. مشخص شود که آیا دو تکلیف SPT و VT در ارتباط با اندازه پردازش خودکار با هم متفاوت هستند. در آزمایش اول، دو تکلیف اجرای عمل و کلامی در دو حالت جداگانه غیرفراگیر دستکاری شدند. در آزمایش دوم، هر دو تکلیف SPT و VT به طور همزمان در یک حالت واحد غیرفراگیر دستکاری شدند. بعلاوه در آزمایش سوم، به آزمودنیها گفته نشد این دو تکلیف را به یاد بسپارند و یا در بارة آزمون حافظة آتی اطلاعی به آنها داده نشد. نتایج هر سه آزمایش نشان داد که روش PDP ، بزار مناسبی برای تمایز بین دو پردازش خودکار (نهان) و کنترل شده (آشکار) نیست و برای موقعیت ها یا برای مواد یادگیری گوناگون تقسیم پذیر نیست. این نتایج، با توجه به نقض دو فرض روش PDP (تغییرناپذیری در آشنایی و تغییرناپذیری در یادآوری) مورد بحث قرار گرفته اند. پرونده مقاله

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