{"id":3853,"date":"2015-12-28T11:48:44","date_gmt":"2015-12-28T11:48:44","guid":{"rendered":"http:\/\/biomedpharmajournal.org\/?p=3853"},"modified":"2020-04-25T03:29:20","modified_gmt":"2020-04-25T03:29:20","slug":"dynamic-1h-nmr-study-of-the-hindered-internal-rotation-in-a-particular-biological-phosphorus-ylide-involving-6-azauracil","status":"publish","type":"post","link":"https:\/\/biomedpharmajournal.org\/staging\/vol8no2\/dynamic-1h-nmr-study-of-the-hindered-internal-rotation-in-a-particular-biological-phosphorus-ylide-involving-6-azauracil\/","title":{"rendered":"Dynamic 1H NMR Study of the Hindered Internal Rotation in a Particular Biological Phosphorus Ylide Involving 6-Azauracil"},"content":{"rendered":"

Introduction<\/strong><\/p>\n

Structure, properties, reactions mechanism and applications of P-ylides and their derivatives especially in the synthesis of naturally occurring products with pharmacological and biological activities are remarkable and important [1-9]. As phosphorus ylides<\/em> from 6-Azauracil is not exception from the principle.<\/p>\n

6-Azauracil or 6-Aza-2, 4-dihydroxypyrimidine is an inhibitor of enzymes that are involved in pyrimidine and purine biosynthesis, which leads to alterations in nucleotide pool levels in inside the body. Afterward the reduction of nucleotide levels by 6-azauracil can reduce transcription elongation [10]. The inhibition of GTP biosynthesis and IMP dehydrogenase activity in Saccharomyces cerevisiae by 6-azauracil has been studied [11]. 6-Aza-2, 4-dihydroxypyrimidine has been widely used in investigations on modulation of transcription, particularly in yeast model systems. In investigations of mutations in components of the RNA polymerase II transcription elongation machinery, 6-azauracil has been presented to induce transcription in wild type Saccharomyces cerevisiae of the PUR5 gene, which is one of four genes that encode IMPDH-related enzymes. It is worth noting mutants which are sensitive to 6-azauracil, for example mutants with a disrupted gene encoding elongation factor SII or containing amino acid substitutions in polymerase II subunits, are also faulty in PUR5 induction [12]. Other investigations on elongation-defective mutant yeast show that 6-azauracil treatment leads to diminished transcription of the GAL1 gene [13]. The addition of Saccharomyces cerevisiae mutants defective in the histone methyl transferase gene Set2 have been shown to have increased talent to 6-azauracil (treatment).<\/p>\n

Some of phosphorus ylides exhibit dynamic 1<\/sup>H NMR effects that affords good information regarding the interchangeable process of rotational isomers that provide important kinetic data, and also it is useful tool when discussing the barriers separating two states that observable by NMR spectroscopy [14-17].<\/p>\n

We wish to describe the dynamic 1<\/sup>H NMR effects on the phosphorus ylide 4 prepared of the reaction between triphenylphosphine 1 and dimethylacetylendicarboxylate 2 in the presence of 6-azauracil 3 that it\u2019s synthesis has been reported previously [18]. The most common methods of determining activation parameters such as classic, Eyring and Arrhenius methods have been employed in the recent research work [19].<\/p>\n

Chemicals and instruments<\/strong><\/p>\n

The chemicals used involving triphenylphosphine 1, dimethyl acetylendicarboxylate 2 and 6-azauracil 3 are all analytical grade, obtained from Fluka (Buchs, Switzerland). The extra pure (supplied by Merk, Darmstadt Germany) including ether and acetone-d6<\/sub>are used throughout the studies. The1<\/sup>HNMR spectra were recorded on a FTNMR 400.22 MHz-BRUKER-Avance III.<\/p>\n

Results and Discussion<\/strong><\/p>\n

The 1<\/sup>H, 13<\/sup>C and 31<\/sup>P NMR spectra of ylide 4 confirmed the presence of two isomers (Fig .1) [21]\n\n\n\n
\"Fig.<\/td>\nFigure 1:\u00a0<\/strong>Synthesis of dimethyl-2-(<\/strong>6-Aza uracil (1-yl)-3-(triphenylphosphoranylidene) butandioate 4 from the reaction between triphenylphosphine 1 and dimethylacetylendicarboxylate 2 with1,5 carbazon 3<\/strong><\/p>\n

Click here to View figure<\/a><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

 <\/p>\n

Moiety of the synthesized compound is strongly conjugated with the adjacent carbonyl group along with the three rotations around the partial carbon\u2013carbon double bond (x), carbon\u2013carbon single (y) and nitrogen\u2013carbon single (z) bonds in the Z<\/em>-4 and E<\/em>-4 rotational isomers (Fig. 2).<\/p>\n\n\n\n
\"Fig.<\/td>\nFigure 2:\u00a0<\/strong>Three possible rotations for the interchangeable processes of the two isomers (Z<\/em>– and E<\/em>-) in ylide 4<\/strong><\/p>\n

Click here to View figure<\/a><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

 <\/p>\n

The 1<\/sup>H NMR spectra of compound 4exhibited two doublets for methine proton (H\u2013C\u2013C=P) at and methyl groups \u03b4 = 5.351-5.402 and 3.622-3.652 ppm, for the minor and major geometrical isomers, respectively. All possible interchangeable process of rotational isomers for ylide 4 involving isomers I, II, III, IV, V and VI are shown in Fig. 3<\/p>\n\n\n\n
\"Figure.<\/td>\nFigure 3:<\/strong> Interchangeable process of rotational isomers for ylide 4 (1) Restricted rotational process (I, II, 343.15K) around the carbon\u2013carbon double bond [entry a] (2)Restricted rotational\u00a0 process around carbon-carbon simple bond (I,III, 211.15 K) [entry b] and (II,IV,213.15 K) [entry c](3) Restricted rotational process (I ,v,241.15 K) [entry d] and (II,VI,243.15K) [entry d] around carbon\u2013nitrogen simple bond.<\/strong><\/p>\n

Click here to View figure<\/a><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

 <\/p>\n

Dynamic effects for the Z-4 and E-4 rotational isomers as a result of the restricted rotational processes (Fig. 3, a, I and II) around the carbon\u2013carbon double bond<\/strong><\/p>\n

The 1<\/sup>H NMR spectrum for the 4-Z and the 4-E (Fig. 3, a, I and II) in acetone at 50 \u00ba C (323.15 K) showed sharp triplet for the methine proton (H\u2013C\u2013C=P, 3JPH<\/sup>) .They are appreciably broadened at 60\u00baC (333.15 K) .This resonance coalescence occurred at near 70 \u00baC (343.15 K) which is relevant to restricted rotational process around carbon\u2013carbon double bond. Another resonance coalescence is accrued at near 64 \u00baC (337.15 K) in relation to the methoxy group.<\/p>\n

The classic method of determining activation energy parameters is through the determination of temperature at which NMR resonance of two exchanging species coalesce [19]. So, the coalescence temperature (T<\/em>c<\/sub>) and isotropic chemical shift (\u2206\u03bd<\/em>) is extracted in conjunction with the maximum peak separation in the low-temperature limit. Investigation of such behavior with respect to the ylide 4 coalescence temperature (T<\/em>c<\/sub> =343.15K) allowed us to also calculate the rotational energy barrier.<\/p>\n

For this process, activation parameters (\u2206H<\/em>\u2021<\/sup>, \u2206S<\/em>\u2021<\/sup> and \u2206G<\/em>\u2021<\/sup>) and kinetic parameters (k<\/em>c<\/sub> and E<\/em>a<\/sub>) are calculated by the classic method and tabulated[1] in Table 1.<\/p>\n[1]: \u2206G<\/em>\u2021<\/sup> = aT<\/em>{9.972 + log(T<\/em>c<\/sub>\/\u2206\u03bd<\/em>) where a<\/em> = 4.575 \u00d7 10-3<\/sup> for unites of kcal\/mol, at the coalescence temperature:kc<\/sub>= \u03c0\u0394\u03c5<\/em>\/\u221a2, \u2206H<\/em>\u2021<\/sup> = \u2206[log(k<\/em>c<\/sub>\/T<\/em>c<\/sub>)]\/\u2206[1\/T<\/em>c<\/sub>], \u2206S<\/em>\u2021<\/sup> = (\u2206H<\/em>\u2021<\/sup> – \u2206G<\/em>\u2021<\/sup>)\/T, E<\/em>a<\/sub> = \u2206H<\/em>\u2021<\/sup> + nRT<\/p>\n

Table 1:\u00a0<\/strong>The activation parameters derived from dynamic review <\/strong>ylide 4<\/strong> around the carbon-carbon double bound (Entry a,<\/strong> Figure 3)<\/strong><\/p>\n\n\n\n\n\n\n\n
T<\/em><\/strong>c<\/sub><\/strong><\/td>\n\u03b4<\/strong><\/td>\n\u2206\u03bd<\/em><\/strong><\/td>\nk<\/em><\/strong>c<\/sub><\/strong><\/td>\n\u2206G<\/em>\u2021<\/sup><\/strong><\/td>\n\u2206H<\/em>\u2021<\/sup><\/strong><\/td>\n\u2206S<\/em>\u2021<\/sup><\/strong><\/td>\nE<\/em><\/strong>a<\/sub><\/strong><\/td>\n<\/tr>\n
K<\/strong><\/td>\nppm<\/strong><\/td>\nHz<\/strong><\/td>\ns-1<\/sup><\/strong><\/td>\nkcalmol-1<\/sup><\/strong><\/td>\nkcalmol-1<\/sup><\/strong><\/td>\ncalmol-1<\/sup>K-1<\/sup><\/strong><\/td>\nkcalmol-1<\/sup><\/strong><\/td>\n<\/tr>\n
343.15<\/td>\n5.351-5.402<\/td>\n20.41<\/td>\n45.32<\/td>\n17.58<\/td>\n<\/td>\n<\/td>\n<\/td>\n<\/tr>\n
<\/td>\n<\/td>\n<\/td>\n<\/td>\n<\/td>\n19.66<\/td>\n6.07<\/td>\n20.34<\/td>\n<\/tr>\n
337.15<\/td>\n3.622-3.652<\/td>\n12.01<\/td>\n26.66<\/td>\n17.615<\/td>\n<\/td>\n<\/td>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

 <\/p>\n

Due to the isotropic chemical shifts of the exchanging species are dependent on temperature,<\/p>\n

So accurately determining of \u2206\u03bd <\/em>is often difficult and thus estimation of the activation energy barrier (\u2206G<\/em>\u2021<\/sup>) has a large error.<\/p>\n

Therefore, to complete analysis and reducing the errors, the determining of activation parameters are performed by Arrhenius plot and Eyring plot methods. With respect to the average value of<\/p>\n[1]: \u2206G<\/em>\u2021<\/sup> = aT<\/em>{9.972 + log(T<\/em>c<\/sub>\/\u2206\u03bd<\/em>) where a<\/em> = 4.575 \u00d7 10-3<\/sup> for unites of kcal\/mol, at the coalescence temperature:kc<\/sub>= <\/strong>\u03c0\u0394\u03c5<\/em>\/\u221a<\/strong>2, \u2206H<\/em>\u2021<\/sup> = \u2206[log(k<\/em>c<\/sub>\/T<\/em>c<\/sub>)]\/\u2206[1\/T<\/em>c<\/sub>], \u2206S<\/em>\u2021<\/sup> = (\u2206H<\/em>\u2021<\/sup> – \u2206G<\/em>\u2021<\/sup>)\/T, E<\/em>a<\/sub> = \u2206H<\/em>\u2021<\/sup> + nRT<\/p>\n

Best results for \u2206S<\/em>\u2021<\/sup> will be obtained by drawing a new plot (Figure 4B), where \u2206S<\/em>\u2021<\/sup> (that is sensible sensor) can be found from the slope. The activation parameters are accumulated in Table 3 for comparing the derived data with the previous data. By picking a temperature (T = 343.15 K) and comparing the magnitudes of \u2206H<\/em>\u2021<\/sup> and T\u2206S<\/em>\u2021<\/sup>, we can decide if the step is enthalpy-controlled or entropy-controlled. For rotation around the carbon-carbon double bond \u2206H<\/em>\u2021<\/sup> = 15.82 kcalmol-1<\/sup> and T\u2206S<\/em>\u2021<\/sup> = -0.0006 kcalmol-1<\/sup>, so enthalpy and entropy are both important and rotation around the double bond is controlled by enthalpy and entropy. This agrees with this process. Because in the rotation around the double bond, leaving solution will involve breaking double bond with solvent (enthalpy) and losing the freedom of the molecule (entropy).<\/p>\n

The standard errors of the Eyring and Arrehnius equations for activation parameters are also calculated[1].This correlation has been mentioned elsewhere [20-22]. The values of activation energy and activation parameters (\u2206G<\/em>\u2021<\/sup>, \u2206H<\/em>\u2021<\/sup>, \u2206S<\/em>\u2021<\/sup>) obtained from three methods are reported in Table 3.<\/p>\n

Table 2:\u00a0<\/strong>Determination \u2206G<\/em>\u2021<\/sup>, lnk\/T and lnk for rotation around carbon-carbon double bond (Entry a, Fig. 3)<\/strong><\/p>\n\n\n\n\n\n\n\n\n
T<\/em><\/strong>c<\/sub><\/strong><\/p>\n

K<\/strong><\/td>\n

1\/T\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/strong><\/td>\n\u2206<\/strong>\u03b4<\/strong><\/p>\n

ppm\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/strong><\/td>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 \u00a0\u00a0\u2206\u03bd<\/strong><\/p>\n

\u00a0 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0Hz<\/strong><\/td>\n

\u00a0\u00a0\u00a0\u00a0 \u2206G<\/strong>\u2021<\/sup><\/p>\n

\u00a0kcal\/mol<\/strong><\/td>\n

Lnk\/T\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/strong><\/td>\nLnk<\/strong><\/td>\nT\u00d7Lnk\/T<\/strong><\/td>\n<\/td>\n<\/tr>\n
 <\/p>\n

293.15<\/td>\n

 <\/p>\n

0.00341<\/td>\n

 <\/p>\n

5.293-5.337<\/td>\n

 <\/p>\n

17.61<\/td>\n

 <\/p>\n

15.10<\/td>\n

 <\/p>\n

-3.40<\/td>\n

 <\/p>\n

2.27<\/td>\n

 <\/p>\n

-996.71<\/td>\n

<\/td>\n<\/tr>\n
303.15<\/td>\n0.00329<\/td>\n5.313-5.360<\/td>\n18.81<\/td>\n15.58<\/td>\n-2.51<\/td>\n3.20<\/td>\n-760.906<\/td>\n<\/td>\n<\/tr>\n
313.15<\/td>\n0.00319<\/td>\n5.334-5.383<\/td>\n19.61<\/td>\n16.07<\/td>\n-1.67<\/td>\n4.08<\/td>\n-522.96<\/td>\n<\/td>\n<\/tr>\n
323.15<\/td>\n0.00309<\/td>\n5.351-5.402<\/td>\n20.41<\/td>\n16.55<\/td>\n-0.88<\/td>\n4.89<\/td>\n-285.34<\/td>\n<\/td>\n<\/tr>\n
<\/td>\n<\/td>\n<\/td>\n<\/td>\nAverage15.82<\/td>\n<\/td>\n<\/td>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

 <\/p>\n[1]: ln(k<\/em>\/T)=23.76+ \u2206S<\/em>\u2021<\/sup>\/R – \u2206H<\/em>\u2021<\/sup>\/RT, slope = – \u2206H<\/em>\u2021<\/sup>\/R and intercept point= \u2206S<\/em>\u2021<\/sup>\/R +23.76,\u00a0 \u2206G<\/em>\u2021<\/sup> = \u2206H<\/em>\u2021<\/sup> – T\u2206S<\/em>\u2021<\/sup>, E<\/em>a<\/sub> = \u2206H<\/em>\u2021<\/sup> + RT<\/p>\n[1]: lnk = lnA \u2013 (E<\/em>a<\/sub>\/R)(1\/T), slope = –E<\/em>a<\/sub>\/R, \u2206H<\/em>\u2021<\/sup> = E<\/em>a<\/sub>– RT<\/p>\n[1]: \u03c3(\u2206S\u2021<\/sup>) = (1\/T<\/em>av<\/sub>)\u03c3(\u2206H<\/em>\u2021<\/sup>) where T<\/em>av<\/sub>= is the center of the temperature range studied, \u03c3(\u2206S\u2021<\/sup>) = \u03c3(\u2206H<\/em>\u2021<\/sup>\u00d70.0034 K-1<\/sup>)<\/p>\n

 <\/p>\n\n\n\n
\"Figure.<\/td>\nFigure 4A:<\/strong>\u00a0An Eyring plot of ln (k<\/em>\/T) versus 1\/T<\/strong><\/p>\n

Click here to View figure<\/a><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

 <\/p>\n\n\n\n
\"Figure<\/td>\nFigure 4B:<\/strong>\u00a0A different linearized form of Eyring equation<\/strong><\/p>\n

Click here to View figure<\/a><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

 <\/p>\n\n\n\n
\"Fig.<\/td>\nFigure 5:\u00a0<\/strong>An Arrhenius plot of ln (k) versus 1\/T<\/strong><\/p>\n

Click here to View figure<\/a><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

 <\/p>\n

Table 3:\u00a0<\/strong>Comparing the obtained results from the three methods (Classic, Eyring and Arrhenius) for the restricted rotation around the carbon-carbon double bond in the isomer Z<\/em>-4 and E<\/em>-4 [entry a]<\/strong><\/p>\n\n\n\n\n\n\n\n
Methods<\/strong><\/td>\n\u2206G<\/em>\u2021<\/sup><\/strong><\/p>\n

\u00a0(kcalmol-1<\/sup>)<\/strong><\/td>\n

\u2206H<\/em>\u2021<\/sup><\/strong><\/p>\n

\u00a0(kcalmol-1<\/sup>)<\/strong><\/td>\n

\u2206S<\/em>\u2021<\/sup><\/strong><\/p>\n

\u00a0(calmol-1<\/sup>K-1<\/sup>)<\/strong><\/td>\n

E<\/em><\/strong>a<\/sub><\/strong><\/p>\n

(kcalmol-1<\/sup>)<\/strong><\/td>\n<\/tr>\n

Classic<\/td>\n17.58<\/td>\n\u00a019.66<\/td>\n6.07<\/td>\n20.34<\/td>\n<\/tr>\n
Eyring A<\/td>\n15.86<\/td>\n\u00a0\u00a0 15.74 \u00b10.32<\/td>\n-0.33 \u00b1 0.001<\/td>\n16.42\u00b10.32<\/td>\n<\/tr>\n
Eyring B<\/td>\n15.83<\/td>\n15.83\u00b10.32<\/td>\n0.00199\u00b1 0.001<\/td>\n16.51\u00b10.32<\/td>\n<\/tr>\n
Arrhenius<\/td>\n15.78<\/td>\n15.66 \u00b10.32<\/td>\n-0.33 \u00b10.001<\/td>\n\u00a016.35\u00b10.32<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

 <\/p>\n

Comparing calculated results (Table 3) using three methods indicate that the results from Eyring and Arrhenius plots were in good agreement, however, were different with the classic method<\/p>\n

Dynamic effect for the 4-Z and 4-E rotational isomers as a result of restricted rotational processes (Fig.3, Z entry b,I and III ,E,entry c, II and IV ) around the carbon\u2013carbon simple bond<\/strong><\/p>\n

Herein, when temperature is reduced down lower than ambient temperature, the 1<\/sup>H NMR spectrum for the 4– <\/em>Z isomer (Fig. 3, b, I and III) in acetone-d6<\/sub> shows a resonance arising from methoxy proton\u00a0 (3. 625-3.640 ppm) which is appreciably broadened comparison with a corresponding singlet which is measured at 10 \u00baC ( 283.15K) . The resonance coalescence occurs at approximately -62 \u00baC (211.15 K) and appears as a singlet resonance at -90 \u00baC (183.15K), the lowest temperature investigated, which is relevant to the restricted rotational process around the carbon\u2013carbon single bond.<\/p>\n

Also, when temperature is reduced down lower than ambient temperature, the 1<\/sup>H NMR spectrum for the 4–<\/em>E isomer (Fig. 3, c, II and IV) in acetone-d6<\/sub> shows a resonance arising from methoxy group ( 3.640-3.765 ppm) which is appreciably broadened comparison with a corresponding a singlet which is measured at 10\u00baC ( 283.15K). The resonance coalescence occurs at approximately -60 \u00baC (213.15 K) and appears as a singlet resonance at -90 \u00baC (183.15K), the lowest temperature investigated, which is relevant to the restricted rotational process around the carbon\u2013carbon single bond. \u00a0For this process, \u2206G<\/em>\u2021<\/sup>, k<\/em>c<\/sub> are calculated and presented in Table 4.<\/p>\n\n\n\n
\"Table<\/td>\nTable 4:\u00a0<\/strong>Activation energy barrier (<\/strong>\u2206G<\/em>\u2021<\/sup><\/strong>) and <\/strong>k<\/em><\/strong>c <\/sub><\/strong>around the carbon\u2013carbon simple bond for isomers Z and E (4-Z Entry b, I, III and 4-E Entry c, II, IV)<\/strong><\/p>\n

Click here to View\u00a0table<\/a><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

 <\/p>\n

Dynamic effect for the 4-Z and 4-E rotational isomers as a result of restricted rotational processes (Fig. 3, Z, entry d, I and V, E, entry e, II and VI) around the nitrogen\u2013carbon (N -C-CH) bond <\/strong><\/p>\n

when temperature is reduced down lower than ambient temperature, the 1<\/sup>H NMR spectrum result for the 4– <\/em>Z isomer (Fig. 3, d, I and V) in acetone-d6<\/sub> shows a resonance arising from methoxy\u00a0\u00a0 (\u00a0 2.996-3.004\u00a0\u00a0 ppm) that is appreciably broadened in comparison with a corresponding doublet that was measured at 20 \u00baC (293.15 K). This resonance coalescence occurred at approximately -32 \u00baC (241.15 K) which is relevant to restricted rotational process around nitrogen\u2013carbon single bond and appears as a doublet resonance at -90 \u00baC (183.15K), the lowest temperature investigated, which is relevant to the restricted rotational process around the nitrogen\u2013carbon single bond.<\/p>\n

Another resonance coalescence is accrued at near -28 \u00baC (245.15 K) in relation to the methine proton (H\u2013C\u2013C=P, 3JPH<\/sup>).<\/p>\n

Also, the 1<\/sup>H NMR spectrum for the 4-E (Fig. 3, entry e, II and VI) in acetone-d6<\/sub> shows a resonance arising from methoxy (3.284- 3.384.15 K ppm) that is appreciably broadened in comparison with a corresponding doublet that was measured at 20 \u00baC (283.15 K) for isomer E. This resonance coalescence occurred at approximately -30\u00baC(243.15K) which is relevant to restricted rotational process around nitrogen\u2013carbon single bond and appears as a doublet resonance at -90 \u00baC (183.15K), the lowest temperature investigated, which is relevant to the restricted rotational process around the nitrogen\u2013carbon single bond. \u00a0Another resonance coalescence is accrued at near-26\u00baC (247.15 K) in relation to the methine proton (H\u2013C\u2013C=P, 3JPH<\/sup>). For this process, the activation parameters involving \u2206G<\/em>\u2021<\/sup>, \u2206H<\/em>\u2021<\/sup> and \u2206S<\/em>\u2021<\/sup>, and kinetic parameters (k<\/em>c<\/sub> and E<\/em>a<\/sub>) obtained using the classic method for 4– <\/em>Z and 4-E<\/em> isomers is reported in Table 5.<\/p>\n

Table 5:\u00a0<\/strong>Activation parameters of phosphorus ylide4for rotation around the nitrogen- carbon single bond in the Z-4 and 4-E isomer, (4-Z<\/strong>, entry d<\/strong>, I, V, and 4-E<\/strong>, entry e,<\/strong> II, VI) according to classic method<\/strong><\/p>\n\n\n\n\n\n\n\n\n\n
isomers<\/em><\/strong>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/em><\/strong>T<\/em><\/strong>c<\/sub><\/strong> (K)<\/strong><\/td>\n\u03b4 (ppm)<\/strong><\/td>\n\u2206\u03bd<\/em> (Hz)<\/strong><\/td>\nk<\/em><\/strong>c<\/sub><\/strong> (s-1<\/sup>)<\/strong><\/td>\n\u2206G<\/em>\u2021<\/sup> (kcalmol-1<\/sup>)<\/strong><\/td>\n\u2206H<\/em>\u2021<\/sup> (kcalmol-1<\/sup>)<\/strong><\/td>\n\u2206S<\/em>\u2021<\/sup> (calmol-1<\/sup>K-1<\/sup>)<\/strong><\/td>\n\n

E<\/em><\/strong>a<\/sub><\/strong> (kcalmol-1<\/sup>)<\/strong><\/p>\n<\/td>\n<\/tr>\n

Z\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 241.15<\/td>\n2.996-3.004<\/td>\n3.2<\/td>\n7.11<\/td>\n13.07<\/td>\n<\/td>\n<\/td>\n<\/td>\n<\/tr>\n
<\/td>\n<\/td>\n<\/td>\n<\/td>\n<\/td>\n12.63<\/td>\n-1.82<\/td>\n13.11<\/td>\n<\/tr>\n
Z\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 245.15<\/td>\n5.08-5.205<\/td>\n5<\/td>\n11.11<\/td>\n13.08<\/td>\n<\/td>\n<\/td>\n<\/td>\n<\/tr>\n
E\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 243.15<\/td>\n3.284-3.384<\/td>\n4<\/td>\n8.88<\/td>\n13.08<\/td>\n<\/td>\n<\/td>\n<\/td>\n<\/tr>\n
<\/td>\n<\/td>\n<\/td>\n<\/td>\n<\/td>\n11.62<\/td>\n-5.99<\/td>\n12.11<\/td>\n<\/tr>\n
E\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 247.15<\/td>\n5.205-5.22<\/td>\n6<\/td>\n13.33<\/td>\n13.10<\/td>\n<\/td>\n<\/td>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

 <\/p>\n

Conclusion<\/strong><\/p>\n

We reported dynamic 1<\/sup>H NMR effects around the three chosen bonds within a synthesized ylide.<\/p>\n

    \n
  1. The three most common methods of determining activation parameters are used to find out which of the methods deviate from each other for carbon-carbon double bond. The results obtained from the Eyring and Arrhenius methods were consistent, however, were different with the classic method.<\/li>\n
  2. Activation parameters were calculated using classic method (single point) for nitrogen\u2013carbon bond for Z isomer and E isomer. The Eyring and Arrhenius method did not use in these rotations because required data were not available.<\/li>\n
  3. The value of activation barrier energy (\u2206G<\/em>\u2021<\/sup>) and kc <\/sub>were calculated for carbon\u2013carbon simple bond for Z isomer and E isomer. The classic method (single point), Eyring and Arrhenius method did not use in these rotations because required data were not available.<\/li>\n
  4. In this study, due to the strong conjugation with the adjacent carbonyl group, the value of activation barrier energy (\u2206G<\/em>\u2021<\/sup>) of the restricted rotation around the partial carbon-carbon double bond (MeO2<\/sub>C=CPPh3<\/sub>) was larger than the nitrogen-carbon (N-C-CH) and carbon-carbon (MeO2<\/sub>CH-C-C=PPh3<\/sub>) single bonds. As a case study, because of the lone pair inversion of nitrogen atom in ring, rotation around the carbon-nitrogen single bond needs a barrier rotational energy more than the carbon-carbon single bond.<\/li>\n
  5. Rotation around the carbon-carbon double bond \u2206G<\/em>\u2021<\/sup> has a more positive value. So high value of \u2206G<\/em>\u2021<\/sup> indicates the rate of this process is slow at room temperature. At higher temperature it is fast and spontaneous.<\/li>\n
  6. Rotation around the carbon-carbon single bond \u2206G<\/em>\u2021<\/sup> has low value (less position value), so rotation around the carbon-carbon single bond is a fast process and spontaneous at room temperature, observation of two conformers (I, II or III and IV) on the basis of this rotation at low temperature is a good evidence for the process that is not spontaneous under this condition.<\/li>\n<\/ol>\n

    Acknowledgement<\/strong><\/p>\n

    We gratefully acknowledge financial support from the Research Council of the University of Sistan and Baluchestan.<\/p>\n

    References<\/strong><\/p>\n

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