CC BY
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ISSN 2522-1841 (Online) ISSN 0005-2531 (Print)
UDC 547.853:620.193+519.677:544.6.004.12
A COMPUTATIONAL STUDY OF SUBSTITUENT EFFECT 1, 3, 4-THIADIAZOLE ON
CORROSION INHIBITION
Hiwa Mohammad Qadr, Dyari Mustafa Mamand
University of Raparin, College of Science, Department of Physics, Sulaymaniyah, Iraq
hiwa.physics@uor.edu.krd
Received 06.10.2022 Accepted 15.03.2023
A theoretical study of 1, 3, 4-thiadiazole with nine various derivatives in gaseous and aqueous phases was investigated by employing the density functional theory (DFT) at 6-311++(d, p) basis set and Becke's three parameters hybrid exchange-correlation functional (B3LYP). The molecules are calculated using quantum computational chemistry calculations such as Gaussian09 software. This paper is to determine the chemical reactivity for various heterocyclic organic compounds and to understand the process of corrosion inhibition. The quantum chemical properties such as the highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO), energy gap (AE), dipole moment global hardness (n), global softness (S), electronegativity (x), electrophilicity (ra), nucleophilicity (e), chemical potential (CP) and electrons transferred from inhibitors to metal surface (AN) were calculated. Dynamic simulation approximations to demonstrate the corrosion inhibition performances of studied inhibitors against the corrosion of 1, 3, 4-thiadiazole in the gaseous and aqueous phases can be given as 1<9<8<3<4<5<6<7<2 and1<3<9<8<3<4<5<6<7<2.
Keywords: 1, 3, 4-thiadiazole, DFT, Corrosion inhibitors, HUMO, LUMO
doi.org/10.32737/0005-2531-2023-2-19-29
Introduction
To prevent corrosion on a metal surface, in acidic and basic solutions corrosion inhibitors are used to reduce the ratio of corrosive. Descaling, cleaning, pickling and acidizing oil wells are all businesses that use hydrochloric acid [1-3]. In acidic solutions, the corrosion inhibitors used are mostly heterocyclic molecules such as sulfur, phosphorous, oxygen, nitrogen, and aromatic or aliphatic organic chemicals, which are adsorbed on the surfaces of metals [4-13]. Due to the vacant d-orbital of iron atoms, the creation of a metal cation among inhibitor molecules as electron donors and metal surface atoms as electron acceptors has been hypothesized in corrosion research. Organic molecules containing nitrogen, sulfur, and oxygen atoms make up the majority of well-known acid inhibitors [14]. Several studies have looked at the effects of nitrogen-containing organic chemicals such as heterocyclic compounds and amines, on steel corrosion in acidic conditions [15, 16]. Several organic inhibitors work via adsorption on the metal surface, according to known evidence. One of the most important considerations for compounds to be effective inhibitors is that they form a compressed barrier film that
they are chemisorbed on the metal substrate. They also have high adsorption energy on the surface of the metal and the barrier layer thus established increases the surface area of the inner layer [1720]. Oxadiazoles have a strong attraction for metal surfaces where they displace water molecules [21]. Furthermore, the oxadiazoles have unshaped electron pairs and a lot of electrons on the oxygen and nitrogen atoms which can react on iron's d-orbitals to form a protective coating [22]. Many N-heterocyclic compounds have been employed to prevent iron or steel from corroding in acidic conditions including pyridazines triazole, [23, 24] purines, [25] thiadiazol, [26] benzimidazoles and [27] pyrazoles [28].
Our present work destined to study molecular geometry, electronic properties and substitution effects of several organic compounds conformed by the substitution of different nu-cleophilic and electrophilic radicals (R1 and R2) in a ring of 1,3,4-thiadiazole using DFT method and carried out by Gaussian09 software.
Theory and computational details
The purpose of our calculation based on DFT at 6-311G++ basis set and B3LYP level is to calculate a lot of chemical parameters [29,
30]. The 6-311G is the standard, split-valence double-zeta basis set the functions use to describe core and valence orbitals, and (d, p) these are polarization functions to describe the chemical bonds, and ++ are diffuse function [31]. Depending on these properties, this basis set 6-311G++(d, p) is very useful and accurate to calculate HOMO, LUMO, hardness, softness, electronegativity, chemical reaction, electrophi-licity, proton affinity and nucleophilicity [32]. The Fukui function analysis indicates the local reactivity of the molecules [33]. From the Mulli-ken charge populations, describe the Fukui function f(r) at a constant potential external v(r) is the derivative of the electronic density p(r) concerning the number of electrons N [34]:
= /P(r)\ (1)
' dN / ^
/ v(r)
fir)
The density of the highest occupied molecular orbital Phomo and the density of the first unoccupied molecular orbital pLUM0 can calculate if the effects of relaxation associated with the removal or addition of electronic charges are not considered, then [35].
P (f) « pLUMo(r) p+(r) « PH0M0(r)
(2a) (2b)
Figure 1 can be shown that Chemical structure of 1,3,4-thiadiazole ring was united to two substituent groups R1 and R2 to give nine different derivatives. These derivatives are (1) 2-methyl-1,3,4-thiadiazole (2) 2-propyl-5-methyl-1,3,4-thiadiazole (3) 2,5-dimethyl-1,3,4-thiadi-azole; (4) 2-ethyl-5-methyl-1,3,4-thiadiazole (5) 2-(2-hidroxy ethyl)-5-methyl-1,3,4-thiadiazole; (6) 2-aminoethyl-5-methyl-1,3,4-thiadiazole; (7) 2-(2-chloroethyl)-5-methyl-1,3,4-thiadiazole; (8) 2-(2-carboxy ethyl)-5-methyl-1,3,4-thiadiazole; and (9) 2-(2-tioethyl)-5-methyl-1,3,4-thiadiazole.
Result and discussion
HOMO, LUMO and frontier orbital gap are significant parameters in quantum computational chemistry [36, 37]. Table 1 shows band gap energies of nine derivatives. The charge-transfer interaction inside the molecule is explained by the energy gap of HOMO-LUMO [38]. Frontier orbitals are the main factors to describe the molecule interacts with other species. The chemical interaction between HOMO-LUMO decides the formation of transition states [39]. The ability of molecules to electron-donating can be found with the energy of EHOMO [40]. If the molecule has a high EHOMO, the tendency to donate an electron will increase to allow acceptor molecules with low energy and empty molecular orbital. Facilitate adsorption of molecules (accordingly inhibition) will increase with the increase in the value of EHOMO due to adsorbed layer were influencing the transportation process [41]. The probability of accepting electrons by the molecules related to the value of ELUMO, the tendency of accepting electrons by molecules will increase with the lower value of ELUMO, the ability to accept will increase. Materials have a good inhibition efficiency if they have lower bandgap energy [42]. The HSAB theory is a significant advancement in quantum chemistry and useful in a variety of theoretical and experimental research involving corrosion inhibitors, chemical equilibrium, complex stability, precipitation titrations and gravimetry.
The operational definition of the hardness depending ionization energy (I) and electron affinity (A) of the system under consideration presented by Parr and Pearson for electronegativity and chemical potential with the light of finite differences.
1 — -ehomo (3)
A — -elumo (4)
I + A X — ( 2 ) (5)
I-A n — ( 2 ) (6)
1 (7)
o — —
n
Fig. 1. 1, 3, 4-thiadiazole ring with substituents R1 and R2.
Using Parr's definition, the electrophilici-ty index (ro) is a global reactivity index similar
to chemical potential and chemical hardness. The electrophilicity index can be defined as [43]
m =
2-q
(8)
Considering the value of bandgap energy of each derivative reduced is the evidence of the rising of the percentage of corrosion inhibition of 1,3,4-thiadiazole with substituents. The hardness and softness of molecules are related to Eluomo-homo and reactivity to a chemical species which depend on bandgap energy. High reactivity to a chemical species indicates a small bandgap [44]. A hard molecule has a low reactive than a soft molecule because a soft molecule has a small Eg [45]. Reactivity and stability of molecules are two parameters that can be determined by measuring the softness and hardness properties of molecules. The harness properties of the materials in a low perturbation of reactions are the resistance to prevent deformation. Inhibition properties of the molecules will climb with an increase in the value of softness. Inhibition efficiency will be highest when the softness is the highest [46].
Tables 1 and 2 shows all calculations were performed with quantum computational chemistry for the derivatives of 1,3,4-thiadiazole in the gas phase. For each of the atoms of derivatives of 1,3,4-thiadiazole molecule, Fukui indices parameters have been calculated.
The calculated values of EHOMO and ELUMO for the investigated derivatives in non-protonated gas are shown in Table 1. The order
of inhibition efficiency of the investigated inhibitors corresponds to the order established from theoretical data based on 1<9<8<3<4< 5<6<7<2. However, based on the results obtained for ELUMO in the gaseous phase, the direction of Elumo is: 1>9>8>3>4>5>6>7>2.
As a function of the reaction of the inhibitor molecule towards adsorption on the metal surface, the energy gap is an important descriptor. The reactivity of the molecule increases with the reduction of AE. It is known that corrosion inhibitors with small energy gaps are effective. Because the ionization energy needed to remove the electron from the final occupied orbital is low. Organic compounds can not only give electrons to empty metallic orbitals but also accept metal-free electrons, according to Bereket et al. [47] are excellent corrosion inhibitors. Furthermore, a molecule with a lower energy gap appears to be more polar-izable and typically characterized by low kinetic stability and strong chemical activity, referred to as a soft molecule. The results in Table 1 can be shown that inhibitor 1 has the smallest energy gap under all conditions which means that the molecule can perform better as a corrosion inhibitor.
Hardness and softness are well-known qualities for determining molecule stability and reactivity. according to Obi-Egbedi, Chemical hardness is defined as the resistance to deformation or polarization of the electron cloud of atoms, ions or molecules under minor perturbations of chemical reactions [48].
Molecules HOMO (eV) LUMO (eV) I A AE (eV) V a CP £
1 -6.2861 -2.1850 6.28615 2.18509 4.1010 2.05053 0.48767 4.23562 -4.235628 4.3745 0.22859
2 -6.8684 -6.4850 6.86847 6.48506 0.3834 0.19170 5.21632 6.67677 -6.6767 116.27 0.00860
3 -7.1555 -3.5951 7.15556 3.59519 3.5603 1.78018 0.56174 5.37537 -5.37537 8.1156 0.12321
4 -7.5808 -5.5582 7.58087 5.55824 2.0226 1.01131 0.98880 6.56956 -6.56956 21.338 0.04686
5 -7.1955 -6.1615 7.19556 6.16152 1.0340 0.51702 1.93415 6.67854 -6.6785 43.134 0.02318
6 -7.3011 -6.3490 7.30114 6.34901 0.9521 0.47606 2.10054 6.82507 -6.8250 48.923 0.02044
7 -6.4091 -5.6156 6.40914 5.61565 0.7934 0.39674 2.52050 6.01240 -6.01240 45.556 0.02195
8 -7.5982 -5.1299 7.59829 5.12993 2.4683 1.23418 0.81025 6.36411 -6.36411 16.408 0.06094
9 -6.6184 -3.9364 6.61840 3.93643 2.6819 1.34098 0.74571 5.27741 -5.27741 10.384 0.09629
A soft molecule has a tiny energy gap, whereas a hard molecule has a big energy gap. As a result, molecules having the lowest global hardness values are projected to be effective corrosion inhibitors for bulk metals in acidic environments. Inhibitor adsorption occurs on a metal surface in the softest and least hard part of the molecule. Table 1 show the calculated values of the gas phases of the analyzed derivatives from 1 to 9. Compared with other inhibitors, 1, 3, 9 and 8 have the highest levels of hardness, according to the calculations. Compared with the derivatives, the data show that inhibitor 1 has the highest stiffness value of 2.05 eV in the non-protonated gas phase.
The relation between global hardness and charge distribution with the analysis of the Fu-kui function results demonstrate more explana-
tion about reaction behaviour of the studies molecules. Fukui function parameters fj+ for the nucleophilic attack, ffor the electrophilic attack and fj for the radical attack were calculated. A high value of the nucleophilic attack site indicates the ability of the molecules to accept electrons which is high, and the molecule will be more able to stabilize additional electrons [49]. The tendency of a molecule to donate electrons describes by the high electro-philic site value. The ability of the metal surface to electron-donating increase indicates increasing the inhibition efficiency. If the ability of the surface of the metal to electron-donate is high, the inhibition efficiency will be increase. Figure 2 shows optimized structures, LUMO and HOMO of non-protonated inhibitor molecules.
Table 2. Calculated Fukui functions and Mulliken atomic charges for derivatives 1-9
Molecules Atoms QN Qn+I f+ f- f0
N4 -0.106 -0.03 -0.130 0.076 0.024 0.05
1 N5 0.065 0.166 -0.034 0.101 0.099 0.1
S6 0.082 0.228 -0.124 0.146 0.206 0.176
N4 0.025 0.061 0.011 0.036 0.014 0.025
2 N5 -0.315 -0.215 -0.329 0.1 0.014 0.057
S6 0.235 0.349 0.209 0.114 0.026 0.07
N4 -0.227 -0.148 -0.254 0.079 0.027 0.053
3 N5 -0.296 -0.218 -0.299 0.078 0.003 0.0405
S6 0.402 1.035 0.332 0.633 0.07 0.3515
N4 0.034 0.039 0.008 0.005 0.026 0.0155
4 N5 -0.354 -0.317 -0.362 0.037 0.008 0.0225
S6 0.266 0.359 0.235 0.093 0.031 0.062
N4 0.070 0.075 0.016 0.005 0.054 0.0295
N5 -0.303 -0.294 -0.312 0.009 0.009 0.009
5 S6 0.194 0.226 0.179 0.032 0.015 0.0235
O16 -0.353 -0.307 -0.365 0.046 0.012 0.029
N4 0.070 0.075 0.016 0.005 0.054 0.0295
N4 -0.144 -0.129 -0.181 0.015 0.037 0.026
6 N5 -0.318 -0.297 -0.331 0.021 0.013 0.017
S6 0.309 0.396 0.290 0.087 0.019 0.053
N16 -0.378 -0.290 -0.479 0.088 0.101 0.0945
N4 0.056 0.058 -0.012 0.002 0.068 0.035
7 N5 -0.237 -0.230 -0.240 0.007 0.003 0.005
S6 0.116 0.200 0.109 0.084 0.007 0.0455
Cl 0.764 0.822 0.639 0.058 0.125 0.0915
N4 -0.016 -0.011 -0.066 0.005 0.05 0.0275
8 N5 -0.250 -0.211 -0.256 0.039 0.006 0.0225
S6 0.195 0.298 0.181 0.103 0.014 0.0585
N4 -0.193 -0.191 -0.239 0.002 0.046 0.024
9 N5 -0.356 -0.321 -0.365 0.035 0.009 0.022
S6 0.253 0.286 0.213 0.033 0.04 0.0365
(6)
(8)
(9)
9»
LUMO
HOMO LUMO
Fig. 2. The optimized structures, LUMO and HOMO of non-protonated inhibitor molecules.
24
O, N, S, and Cl have been shown in Mul-liken charge and Fukui function calculations for ease of understanding and also to determine the effect of each of the atoms on the molecule. For this purpose, using Gaussian software can predict or describe the properties of organic compounds. In this case, the polarized continuum method (PCM) was used [50]. The solute is located in a cavity of roughly molecular form. For
determining the effect of solvent on optimization geometric calculation, the solvent in these models is defined by a continuum that interacts with charges on the cavity surface [51]. Table 3 shows molecular properties of compounds 1-9 in aqueous phase. Table 4 show calculated Fukui functions and Mulliken atomic charges for derivatives 1-9 in aqueous phase.
Table 3. Molecular properties of compounds 1-9 in aqueous phase
Molecules HOMO (eV) LUMO (eV) I A AE (eV) a X CP m £
1 -8.26307 -4.0488 8.26307 4.04881 4.21426 2.10713 0.47457 6.15594 -6.1559 8.992 0.11120
2 -7.59611 -7.1969 7.59611 7.19692 0.39919 0.19959 5.01009 7.39652 -7.3965 137.04 0.00729
3 -7.23093 -5.7757 7.23093 5.77579 1.45514 0.72757 1.37443 6.50336 -6.5033 29.065 0.03440
4 -6.82249 -4.9440 6.8224 4.94407 1.87841 0.93920 1.06472 5.88328 -5.8832 18.426 0.05426
5 -6.44425 -5.4951 6.4442 5.49511 0.94914 0.47457 2.10716 5.96968 -5.9696 37.546 0.02663
6 -6.59527 -5.5862 6.59527 5.58626 1.00900 0.50450 1.98214 6.09077 -6.0907 36.766 0.02719
7 -6.40914 -5.6156 6.4091 5.6156 0.7934 0.3967 2.5205 6.01240 -6.0124 45.556 0.02195
8 -6.81324 -4.4303 6.8132 4.4303 2.3829 1.1914 0.8393 5.6217 -5.6217 13.262 0.07539
9 -6.61840 -3.9364 6.6184 3.9364 2.6819 1.3409 0.7457 5.2774 -5.2774 10.384 0.09629
Table 4. Calculated Fukui functions and Mulliken atomic charges for derivatives 1-9 in aqueous phase
Molecules Atoms QN+I Qn-I f+ r
1 N4 -0.288 -0.114 -0.333 0.174 0.045 0.1095
N5 -0.219 -0.205 -0.238 0.014 0.019 0.0165
S6 0.633 1.189 0.575 0.556 0.058 0.307
2 N4 0.033 0.061 0.011 0.028 0.022 0.025
N5 -0.212 -0.215 -0.329 -0.003 0.117 0.057
S6 0.248 0.349 0.209 0.101 0.039 0.07
3 N4 -0.511 -0.441 -0.535 0.07 0.024 0.047
N5 -0.519 -0.430 -0.535 0.089 0.016 0.0525
S6 0.804 1.450 0.761 0.646 0.043 0.3445
4 N4 0.034 0.039 0.008 0.005 0.026 0.0155
N5 -0.354 -0.317 -0.362 0.037 0.008 0.0225
S6 0.266 0.359 0.235 0.093 0.031 0.062
5 N4 0.070 0.075 0.016 0.005 0.054 0.0295
N5 -0.303 -0.294 -0.312 0.009 0.009 0.009
S6 0.194 0.226 0.179 0.032 0.015 0.0235
O16 -0.353 -0.307 -0.365 0.046 0.012 0.029
6 N4 -0.144 -0.129 -0.331 0.015 0.187 0.101
N5 -0.318 -0.297 -0.181 0.021 -0.137 -0.058
S6 0.309 0.369 0.290 0.06 0.019 0.0395
N16 -0.378 -0.290 -0.479 0.088 0.101 0.0945
7 N4 0.056 0.058 -0.012 0.002 0.068 0.035
N5 -0.237 -0.230 -0.240 0.007 0.003 0.005
S6 0.116 0.200 0.109 0.084 0.007 0.0455
Cl12 0.764 0.822 0.639 0.058 0.125 0.0915
8 N4 -0.016 -0.011 -0.066 0.005 0.05 0.0275
N5 -0.250 -0.211 -0.256 0.039 0.006 0.0225
S6 -0.195 0.298 0.181 0.493 -0.376 0.0585
9 N4 -0.193 -0.191 -0.239 0.002 0.046 0.024
N5 -0.356 -0.321 -0.365 0.035 0.009 0.022
S6 0.253 0.286 0.213 0.033 0.04 0.0365
The bond distance from the analyses of the optimized geometry between C2 and R2 has remained unchanged (1.54 A). The internal ring of 1,3,4-thiadiazole bond angle for S6-C2-N4 and S6-C2-N4 are 111.10865 and 111.10866. At the first derivative, the difference between them is very small, at the second derivative is 0.0060. The bond angle between C1-N4 and C2-N4 are in the same range which are about 1.349830 and 1.349820 at all derivatives, the bond length between C1-N4 and C2-N4 present shows just small variations, and for this purpose, it is reasonable to arrange that all the derivatives performed a length of C1-N4 and C2-N4 bond of 1.34 A0. As far as, the bond distance between S6-C1 and S6-C2 is 1.758050 for each one of all optimized geometry calculations which has the same value indicating the formation of single bonds between them.
The inhibitor with the lowest global hardness is likely to have the best inhibition efficiency. The following anticorrosion efficiency rating has been predicted as a result of our work: inhibitor 2 is higher than inhibitor 7, inhibitor 5 is higher than inhibitor 6 and inhibitor 9 is higher than inhibitor 1.
Electrophilic (m) is a measure of how willing a chemical species is to accept electrons. The higher the value of electrophilicity, the greater the ability of the molecule to receive electrons. On the other hand, low values of chemical potential and electrophilicity describe good nucleophiles, while high values of electro-philicity and chemical potential characterize good electrophiles. The compounds have low electrophilic index values and are good nucleophiles as shown in Tables 1 and 2. Given the electrophilic and nucleophilic data in Table 3, the corrosion inhibition efficiency rating of the
investigated compounds can be determined as follows 1<9<8<4<3<6<5<7<2.
When two systems with different electronegativities such as iron and inhibitor; the electron will be transferred from low electronegativity towards higher electronegativity. Until the chemical potentials or electronegativities are the same. The number of electrons transferred, ANmax, were calculated using the formula [52]. . .f _ XFe — Xinh
mX = 2(VFe-Vinh) (9)
Where xFe is the electronegativities of iron metal which was used xFe = 7 eV and xinh is the electronegativities of inhibitor. and ^inh are the global hardness of iron and the inhibitor molecule. The value of a global hardness is ^Fe = 0 for computation of electron transferred, by assuming that for a metallic bulk I = A [53].
Tables 5 and 6 show quantum chemical parameters of derivatives 1-9 in gas and aqueous phase. The positive number ANmax indicates that the molecules are electron acceptors, while the negative number of ANmax indicates that the molecules are electron donors. As a result, as the electron-donating capacity of these inhibitors increases on the metal surface, the inhibition efficiency increases, too. As the electron-donating ability at the metal surface increases, the inhibition efficiency increases if ANmax < 3.6. The molecules under investigation, except for 1-9 derivatives in the gas and aqueous phases and the B3LYP/6-31++ G(d,p) theoretical plane act as electron donors. The inhibitor molecules' capacity to accept electrons is in the sequence 7 >2>1>9>3>5>8>4>6 in the gas phase and 7>8>9>6>4>8>3>1>2 in aqueous phase. Inhibitor 2 is a donor compound in the aqueous phase.
inhibitors 1 2 3 4 5 6 7 8 9
AN 0.674 0.843 0.456 0.212 0.310 0.183 1.244 0.257 0.642
AEh-d -0.512 -0.047 -0.445 -0.252 -0.129 -0.119 -0.099 -0.308 -0.335
Table 6. Quantum chemical parameters of derivatives 1-9 in aqueous phase
inhibitors 1 2 3 4 5 6 7 8 9
AN 0.200 -0.99 0.341 0.594 1.085 0.901 1.244 0.578 0.642
*Eh-d -0.526 -0.049 -0.18 -0.23 -0.118 -0.126 -0.099 -0.297 -0.335
The chemical interaction between the inhibitors and the metal surfaces depends on the back-donation process which was proposed by Gomez et al. [54], in the light of the charge transfer model for donation and back-donation. According to this theory, if back-donation from the molecule and electron transfer to the molecule occurs at the same time, the energy change is proportional to the molecule's hardness from the following expression [55].
AEb-d = -4
(10)
Back donation from the molecule to the metal is energetically favored between two options when AEh_ri > 0 or AEh_ri < 0. On the me-
tal surface, if higher adsorption of the molecule enhances inhibition effectiveness. Then, the inhibition efficiency should increase with the increase in the stabilization energy induced by the contact between inhibitor and metal surface. In this work, the calculated AEh-d values exhibit the tendency: 2>7>5>6>4>8>9>3>1 in gas phase and aqueous phase is : 2>7>5>6>3>4>8>9>1 as shown in Tables 5 and 6.
In Tables 1 and 3, a series of properties calculated for each one of the derivatives in gaseous and liquid phase are presented. Consequently, the reactivity sequence for the derivatives in the liquid and gas phase are: 1<9<8<4< 3<6<5<7<2 and 1<9<8<3<4<5<6<7<2.
2-methyl-1,3,4-thiadiazole has a high hardness in gas and aqueous phase, besides 2-propyl-5-methyl-1,3,4-thiadiazole has the lowest value of hardness. Tables 2 and 4 describe the Fukui indices which are more significant to predict the lowest and highest susceptible site for electrophilic attack. The most susceptible sites are N4 and S6. N4 and N16 have the highest amount in 2-aminoethyl-5-methyl-1,3,4-thiadiazole in the aqueous phase which they are equal to 0.187 and 0.101. In the gas phase calculations, the Cl atom in 2-(2-chloroethyl)-5-methyl-1,3,4-thiadiazole and N16 in 2-aminoethyl-5-methyl-1,3,4-thiadiazole has the maximum value of f- which are 0.125, 0.101, respectively and most susceptible sites for elec-trophilic attacks.
(1)
(6)
(7) (8) (9)
Figure 3. The optimized structures, HOMOs of non-protonated inhibitor molecules
Conclusion
DFT is used for quantum computational chemistry with B3LYP/6-311G++(d,p) basis set. Quantum chemical computations were performed for both the gas phase and aqueous solution for the non-protonated stated compounds. HOMO and LUMO are helpful to find parameters such as hardness, softness, ionization energy, bandgap energy, electrophilicity, nucleo-philicity and electronegativity of molecules and to indicate chemical reactive behaviour. High softness and low band gap energy indicate the interaction between 1, 3, 4-thiadiazole and inhibitor substituent. The theoretical result showed that the corrosion inhibition performances of studied inhibitors against the corrosion of 1,3,4-thiadiazole in gaseous and aqueous phases can be presented as 1<9<8<3<4<5<6<7<2, 1<3<9<8 <3<4<5<6<7<2, respectively. The conclusion can be shown that N4 has a more reactive site in gaseous and aqueous phases of these derivatives.
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1, 3, 4-TÍADÍAZOL OVOZLOYÍCíLORINÍN KORROZÍYAYA QAR§I TOSÍRINÍN ÖYRONiLMOSi
Hiva Mohammad Qadr, Dyari Mustafa Mamand
Qaz va sulu fazalarda doqquz müxtalif törama ila 1,3,4-tiadiazolun nazari tadqiqi 6-311++(d,p) baza dastinda sixliq funksional nazariyyasi (DFT) va Becke üglü parametrli hibrid mübadilasiindan istifada etmakla aparilmüjdir -korrelyasiya funksionali (B3LYP). Molekullar Gaussian09 proqram taminatlii kimi kvant hesablama kimyasi hesablamalarindan istifada etmakla hesablamr. Bu maqala müxtalif heterosiklik üzvi birla§malarin reaktivliyini müayyan etmak va korroziyaya mane olma prosesini ba§a dü§mak ügün nazarda tutulmu§dur. On yüksak dolmu§ molekulyar orbital (HOMO), an a§agi bo§ (bo§) molekulyar orbital (LUMO), enerji bo§lugu (AE), dipol momenti (д), qlobal sartlik (n) kimi kvant kimyavi xassalari hesablanmi§dir: qlobal yum§aqliq (S), elektronmanfilik (x), elektrofillik (ю), nukleofillik (e), kimyavi potensial (CP) va inhibitorlardan metal sathina (AN) ötürülan elektronlarin sayi. Qaz va su fazalarinda tadqiq edilmi§ korroziya inhibitorlari 1, 3, 4-tiadiazol tarafindan korroziyanin qar§isimn alinmasinin effektivliyini nümayi§ etdirmak ügün dinamik simulyasiya yaxinla§malari 1<9<8<3<4<5<6<7<2 va 1 <3<9< 8<3<4<5<6<7<2 kimi taqdim edila bilar.
Agar sözlzr: 1,3,4-tiadiazol, DFT, korroziya bngidicibri, VZMO, NSMO.
РАСЧЕТНОЕ ИССЛЕДОВАНИЕ ВЛИЯНИЯ ЗАМЕСТИТЕЛЯ 1, 3, 4-ТИАДИАЗОЛА НА
ИНГИБИРОВАНИЕ КОРРОЗИИ
Хива Мохаммад Гадр, Дияри Мустафа Маманд
Теоретическое исследование 1, 3, 4-тиадиазола с девятью различными производными в газовой и водной фазах было проведено с использованием теории функционала плотности (DFT) в базовом наборе 6-311 ++ (d, p) и трехпараметрического гибридного обмена Бекке - корреляционный функционал (B3LYP). Молекулы рассчитываются с использованием расчетов квантовой вычислительной химии, таких как программное обеспечение Gaussian09. Эта статья предназначена для определения химической активности различных гетероциклических органических соединений и понимания процесса ингибирования коррозии. Были вычислены квантово-химические свойства, такие как высшая занятая молекулярная орбиталь (ВЗМО), низшая свободная (незанятая) молекулярная орбиталь (НСМО), энергетическая щель (AE), дипольный момент (д), глобальная жесткость (n), глобальная мягкость (S), электроотрицательность ( x), электрофильность (ю), нуклеофильность (e), химический потенциал (CP) и количество электронов, перенесенных с ингибиторов на поверхность металла (AN). Аппроксимации динамического моделирования для демонстрации эффективности ингибирования коррозии изученными ингибиторами коррозии 1, 3, 4-тиадиазола в газовой и водной фазах могут быть представлены как 1<9<8<3<4<5<6<7<2 и1<3<9<8<3<4<5<6<7<2.
Ключевые слова: 1, 3, 4-тиадиазол, ДФТ, ингибиторы коррозии, ВЗМО, НСМО.
