Structure determination of substituted benzenes by proton magnetic resonance.  Empirical treatment of substituent effects and their utility in predicting chemical shifts

Since the work by Allan ( 1 , Z ) and Robinson ( 3 ) , organic solvents have been used for increasing sensitivities of analysis in atomic absorption spectrophotometry. The most widely used solvent is 4-methyl-2-pentanone (or methyl isobutyl ketone, MIBK). However, its partial solubility in the aqueous phase can be a problem when extracting standards and samples a t different organic-to-aqueous ratios. Previous unpublished work in this laboratory indicated that 3-heptanone might be a possible alternative to MIBK. The former is less soluble in water than the latter and metal chelates are extracted equally well. This report includes the following: the solubility of the two solvents in water and ammonium citrate solutions of varying concentration a t 25 "C; the effect of the solubility of the ketone in the aqueous phase on extraction of lead a t different ratios of organic to aqueous phases; and the efficiency of nebulization of the two solvents. The chelate lead (diethyldithio-carbamate12 was chosen for the ratio experiment as it was a part of a larger study on the effect of hydrogen ion concentration on the determination of lead by solvent extraction and atomic absorption. The solubility in ammonium citrate was studied as citrate is often used as a buffering or masking agent. EXPERIMENTAL Apparatus.A Perkin-Elmer model 403 atomic absorption spectrophotometer with a Fisher Scientific Co. neon filled lead hollow cathode lamp was used for atomic absorption measurements using the 283.3-nm absorbing line of lead. The spectrophotometer is equipped with a laminar flow burner atomizer and a single 4-inch slot burner head. A double "propeller" bladed flow spoiler is attached within the atomizer chamber. Flow rates used were 14.4 I./ min for air and 1.2 l./min for acetylene while aspirating MIBK and 1.6 l./min while aspirating 3-heptanone. Instrument settings were as recommended by the manufacturers optimized for the analysis.L V absorption measurements were made on a Cary Model 14 recording spectrophometer. Reagents. MIBK and 3-heptanone (Matheson, Coleman andBell) and 2-octanone (Eastman Kodak) were distilled from all glass apparatus. 20% Ammonium Citrate. Four hundred grams of ammonium citrate, dibasic, (Baker Analyzed Reagent) were dissolved in 500 ml of double deionized water and neutralized with 128 ml of ammonium hydroxide to the end point of cresol red (pH 7.2). Then 25 ml of 0.496 sodium diethyldithiocarbamate (NaDDC) and 100 ml of 3-heptanone or MIBK were added. The mixture was shaken in a 2-liter separatory funnel for one minute and the phases were allowed to separate. After the upper ketone layer was discarded, another 100-ml ketone extraction was performed. The aqueous layer was then removed and diluted to 2 liters with double deionized water. A third batch was prepared without extraction for use in the solubility studies.Stoch Lend Solution (1000 Fglrnl). Lead nitrate, 1.6985 gram (Pb(N03)2 Baker Analyzed Reagent) purified by recrystalization ( 4 ) , was dissolved in double deionized water, diluted to 1 liter, ...

Section: Resultsmentioning

confidence: 99%

“…" Percent of solvent reaching the flame. C2H2 flow rate 1.6 1./ min; air flow rate, 14.4 l./min 6. Methyl isobutyl ketone.…”

mentioning

confidence: 99%

3-Heptanone vs. 4-methyl-2-pentanone as extracting solvents in atomic absorption spectrophotometry

Everson¹,

Parker²

1974

“…The 6proton value, however, is unique since it is meta to the substituent but has an intervening ring nitrogen which "2-1 secondary value 1calculated from 2-1, 3-OH pyridine. 6 2-NO2 secondary value taken from 2-NOa, 3-•OH pyridine.…”

Section: Resultsmentioning

confidence: 99%

“…(7). 6 The first number indicates the position of the substituent (x). The second number indicates the number of the proton affected.…”

Section: N02 H4mentioning

confidence: 99%

Use of shielding parameters for the calculation of chemical shifts in the nuclear magnetic resonance spectra of substituted pyridines

Zanger¹,

Simons²

1974

The ketone, 2-octanone, was added to relate efficiency of nebulization to boiling point of the organic solvent. As can be seen from Table II, the lower the boiling point, the greater the volatility, the higher the efficiency of nebulization.3-Heptanone is proposed as an alternative solvent to MIBK for the extraction of metal chelates in atomic absorption analysis, particularly when the solubility of MIBK in the aqueous phase is of concern. MIBK is 4.5 times more soluble in aqueous phase at 25 °C than 3-heptanone. The greater efficiency of nebulization of MIBK, on the other hand, should be taken into consideration when the sensitivity of a procedure is important.

“…This is clearly not true for the Mg2+ form of the acrylic resin reported here and Dowex 50 W-8X, and may not be true for other resins. the principle of additivity often yields results which are precise enough for the purpose of determining the substituent patterns in polysubstitued benzenes (13,14).…”

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confidence: 99%

Estimation of the chemical shifts of aromatic protons using additive increments

Beeby¹,

Sternhell²,

Hoffman-Ostenhof³

et al. 1973

The data summarized in Table I indicate that and the internal molality show a significant variation with temperature. However, the molar shift is virtually independent of temperature. This implies that the water released from the resin at higher temperature originates from the bulk water in the resin and not from the cation hydration sphere. The molar shift, 0.215 ppm, is somewhat larger than has been reported for styrene based cation resin (3, 4) and for that recently reported for Mg2+ ion in water, 0.153 ppm (5).If one looks carefully at the spectra obtained at 21.5 °C, a small peak can be seen at approximately the chemical shift of water outside the resin. We estimated that this small peak is approximately 1% of the major water peak. It could result from either a small temperature effect or residual water which is not removed via the centrifuge method. No matter which explanation is indeed correct, the relative intensity implies that the centrifuge method is highly effective for isolating the hydrated resin.(4) D.