Geometric constructions for all the possible isomers of fluorinated pyridines were optimized at the degree of theory. Aromaticities of the considered molecules were investigated utilizing different indices included geometry-based ( HOMA and Bird ( I6 ) ) , magnetism-based ( NICS ( 1 ) and diamagnetic susceptibleness anisotropy ( ) ) , – and ?- negatron count-based ( pEDA, sEDA ) , and late introduced electronic-based ( electric field gradient ( EFG ( 0 ) , EFG ( 0.5 ) ) and Shannon aromaticity ( SA ) ) indices. Furthermore we used besides HOMO-LUMO spread, atomisation energy ( ) , and interaction energy for fluorinated pyridine composites by H2O molecule as planetary forms, and the electric field gradient values ( EFGC-F ( 0 ) ) on the in-between points of C-F bonds and ?-electron population ( N? ) of N atom as local forms. All studied indices except HOMA and EFG ( 0.5 ) are good correlated to each other and to planetary and local forms.
Keywords Fluorinated pyridines · Aromaticity · HOMA · NICS · pEDA · EFG
A great figure of illustrations have been reported that the debut of a fluor or fluorinated groups into an organic molecule induces dramatic alteration in its chemical, physical, and besides pharmacological belongingss [ 1-4 ] . The alone belongingss of fluoroorganic molecules may originate from the belongingss such as ( I ) the greatest electronegativity of fluor atom, ( two ) the largest strength of the carbon-fluor bond, ( three ) the hardness and the low new wave der Waals interaction due to the low polarizability, ( four ) the increased hydrophobicity, and ( V ) the 2nd smallest atomic size of the fluor atom [ 5 ] . These factors are effectual singly or sometimes hand in glove to impact the pharmacological belongingss of the fluorinated molecules [ 6 ] . Fluorinated pyridines are used as an intermediate for fabricating man-made organic, liquid crystals, pharmaceuticals ( antihistamine drug, pheniramine, the antiarrhythmic, disopyramide ) and agrochemicals ( antifungals, weedkillers ) [ 3,5-8 ] , and as starting stuffs for the readying of powerful radioligands for in vivo imagination by antielectron emanation imaging ( PET ) [ 9 ] . Some of fluorinated pyridines were studied before by utilizing FTIR, Raman, NMR spectrometries and ab initio computations [ 10-15 ] . Their crystal constructions were solved by X-ray diffraction experiments [ 16, 17 ] .
On the other manus about 50 % of all the known organic molecules may be identified by aromatic character. Aromaticity is an of import and utile construct in explicating the constructions, stablenesss, and responsivenesss of different molecules. Since aromaticity is expressed by combination of belongingss of molecule, it is normally discussed in footings of energetic [ 18 ] , structural [ 19 ] , magnetic [ 20-22 ] and electronic standards [ 23 ] . These standards lead to energy- , geometry- , magnetic- and electronic-based aromaticity indices. Note that, aromatic compounds can non be to the full characterized by merely one index due to multidimensionality of aromaticity. Therefore, to do dependable comparings restricted to groups of comparatively similar compounds it is normally recommended to use a set of aromaticity indices [ 24-26 ] .
In this survey we have evaluated the geometrical and electronic belongingss of fluorinated pyridines. The comparative and atomisation energies, frontier molecular orbitals, interaction energy for the fluorinated pyridine composites by H2O molecule, and good known different aromaticity indices have been obtained with quantum chemical computations. Those collected informations were analyzed and used to show fluor permutation consequence on the pyridine ring.
It is widely accepted that aromaticity has a mensurable consequence on the electronic energy of aromatic molecules [ 18 ] . Energy needs some sort of mention province, and in consideration of aromaticity the energetic computations ( e.g. , aromatic Stabilization Energy ( ASE ) ) depend to a great extent on the pick of a proper mention, therefore it is someway non dependable [ 27 ] . But, the highest occupied molecular orbital ( HOMO ) – lowest unoccupied molecular orbital ( LUMO ) chitchat and atomisation energy being as planetary forms can besides be used to foretell the aromaticity of the molecules without a mention. The atomisation energy of molecule is calculated as [ 28 ]
( 1 )
where and are the single energies of all atoms in the molecule and the entire energy of the molecule, severally, and is the zero-point vibrational energy rectification.
Variation in geometry is a really of import beginning of information about aromaticity [ 29 ] . Structural aromaticity indices, e.g. harmonic oscillator theoretical account of aromaticity ( HOMA ) [ 19,30 ] and Bird index ( I6 ) [ 31 ] , step the grade of the aromaticity of a molecule by comparing the extent of bond length equalisation in that molecule with a conjectural mention. The HOMA index is defined in such a manner to give 0 for a theoretical account not aromatic system and 1 for a system where full ?-electron delocalization occurs. It is applied to quantify the extent of ?-electron delocalization of 6-membered heterocyclic compounds. HOMA can be calculated by the undermentioned expression:
. ( 2 )
In this equation, N is the figure of bonds considered, and is an empirical invariable ( for C-C and C-N bonds and 93.52, severally ) fixed to hold HOMA=0 for a theoretical account nonaromatic system, and HOMA=1 for a system with all bonds equal to an optimum value Ropt ( 1.388 and 1.334 & A ; Aring ; for C-C and C-N bonds, severally ) , which is assumed to be achieved for to the full aromatic system. Ri stands for a running bond length. Finally, EN and GEO parts of the HOMA index describe a lessening in aromaticity due to bond elongation and bond alternation, severally. Another attack to mensurate aromaticity based on geometry was devised by Bird [ 31 ] which proposed the computation of aromaticity index I6 ( 6-membered ring ) . This index takes into history the grade of statistical uniformity of the bonds orders of the ring but uses the differences between the existent bond orders and arithmetic mean of these bond orders as follows:
( 3 )
R is observed bond length, N is the single bond order, is the average bond order, N is figure of bonds, VK ( 33.2 for 6-membered ring ) , a ( 6.80 and 6.48 for C-C and C-N bonds, severally ) and B ( 1.71 and 2.0 for C-C and C-N bonds, severally ) are invariables [ 31 ] .
Magnetic standards are based on this fact that ?-electron pealing current is induced when the system is exposed to an external magnetic field. One of the most common used magnetic-based indices, which is proposed by Schleyer and coworkers [ 32 ] , is the Nucleus Independent Chemical Shift ( NICS ) . This index is defined as the negative value of the absolute screening which is computed at the centre ( NICS ( 0 ) ) or at some other points of a cyclic system ( NICS ( R ) ) . For illustration NICS ( 1 ) is defined as the computed negative value of the absolute magnetic shielding at 1 & A ; Aring ; over the ring plane. Another magnetic-based index is diamagnetic susceptibleness anisotropies, defined as:
( 4 )
where, and are the three chief constituents of the diamagnetic susceptibleness [ 33 ] . An advantage of this index is its independency of the mention system. The more negative are the NICS and value, the more aromatic is the system.
The electronic construction of the molecule is evidently strongly connected to its aromaticity. The atoms in molecules ( AIM ) parametric quantities, such as pealing critical point ( RCP ) , bond critical point ( BCP ) , electron localisation ( LIs ) and delocalization ( DIs ) , are used for appraisal of ?-electron delocalization [ 34 ] . Recently a new electronic-based aromaticity index ( alleged Shannon aromaticity ( SA ) ) [ 35 ] is introduced by utilizing the definition of Shannon Entropy [ 36 ] and the obtained negatron densenesss at the BCPs of a molecule ( ) . The SA index is defined as
( 5 ) where N is the figure of bonds in the ring, and pi is the normalized negatron denseness at bond critical point ( BCP ) of the ith bond:
The smaller the SA index, the more aromatic is the molecule. The scope 0.003 & A ; lt ; SA & A ; lt ; 0.005 is considered as a boundary between aromatic and antiaromatic systems [ 35 ] .
Many of the discernible belongingss of a molecule are determined in whole or in portion by the simple 3-dimensional negatron denseness distribution. For case, the electric field gradient tensor, which is defined by the 2nd derived functions of the possible generated by electron denseness with regard to desired place of molecule, is proposed by Pakiari and Bagheri [ 37 ] to measure the aromaticity of the molecules. This new electronic-based aromaticity index is called EFG ( electric field gradient ) . The EFG computations in the center and above the bonds in the ring have been done by utilizing prop=EFG Gaussian keyword. EFG values for the two arbitrary points of the center of bond distance, at the zero point ( EFG ( 0 ) ) and at 0.5 & A ; Aring ; above the bond ( EFG ( 0.5 ) ) , have been chosen for all considered molecules in this survey. This is similar to the points of 0.0 and 1.0 in NICS index by Schleyer [ 32 ] . The more positive is the EFG value, the more aromatic is the system. For the antiaromatic molecules EFG value is negative [ 37 ] .
The ?- and ?- negatron count based aromaticity indices pEDA and sEDA were similar in that the former was calculated by summing the 2pz natural atomic orbital tenancies of the pyridine ring atoms and deducting 6, therefore bespeaking how much the ? population of the pealing perverts from the ideal sestet, whereas the latter was calculated by summing the s, post exchange, and py natural atomic orbital tenancies of the pyridine ring atoms and deducting 6, therefore bespeaking how much the ? population of the pealing perverts from the ideal sestet [ 38 ] :
( 6 )
, ( 7 )
where ?i and ?i are the ith 2pz and amount of s, post exchange, and py natural atomic orbitals of the molecule, severally.
All computations on the fluorinated pyridines are carried out utilizing the Gaussian 09 revision-C01 bundle of codifications [ 39 ] . Their geometries are optimized at the B3LYP/6-311++G ( vitamin D, P ) degree. Vibrational frequences are besides calculated to verify that the optimized constructions are local lower limit on the possible energy surfaces. For the electronic energies, HOMO and LUMO of the fluorinated pyridines, individual point computations at the MP2 ( FC ) /6-311++G ( vitamin D, P ) degree are performed on all B3LYP optimized constructions to obtain improved electronic energies. The atomisation energy values are calculated at the B3LYP/6-311++G ( vitamin D, P ) degree for comparing. NICS values are obtained within the gauge independent atomic orbital ( GIAO ) method at B3LYP/6-311++G ( vitamin D, P ) degree. The NICS investigation ( Bq ) is placed at 1 & A ; Aring ; above the ring centre perpendicular to the ring plane due to the best step of the ?-electron delocalization in a cyclic molecule [ 40 ] . Similar to NICS process, the EFG values are obtained utilizing prop=EFG Gaussian keyword. Using the optimized constructions, diamagnetic susceptibleness anisotropies ( ) values are calculated at the HF/6-311++G ( vitamin D, P ) degree. NBO analysis is besides done by NBO 5.G plan interfaced to Gaussian [ 41 ] . The interaction energy of the composites are calculated utilizing supramolecular attack corrected for footing set superposition mistake ( BSSE ) harmonizing to Boys Counterpoise method [ 42 ] , at the B3LYP/6-31+G ( vitamin D, P ) degree. All AIM computations in this survey are performed and visualized utilizing the Multiwfn plan [ 43 ] . The wavefunction-extended ( wfx ) files used for the AIM analysis are prepared utilizing the C01 release of Gaussian 09.
Consequences and treatment
Geometric stuctures and abbreviations of the fluorinated pyridines are depicted in Fig. 1. Since dependable theoretically obtained molecular geometries can be used to measure for geometry-based aromaticity indices [ 44 ] , we have considered deliberate geometrical parametric quantities of fluorinated pyridines. Note that our computations refer to title compounds in gas stage. Selected geometric parametric quantities for fluorinated pyridine derived functions are listed in Table 1.
Relative energetics, frontier orbital energies and chemical hardness
The comparative electronic energies and atomisation energies of all possible isomers of fluorinated pyridines and pyridine are given in Table 2. As seen from Table 2 the most stable isomers in the mono- , di- , tri- , and tetrafluorinated species are 1F2, 2F4, 3F5, and 4F1 isomers, severally harmonizing to calculated electronic and atomisation energy values. The stableness order of species of fluorinated pyridines is found to be as 1F & A ; lt ; 2F & A ; lt ; 3F & A ; lt ; 4F & A ; lt ; 5F by utilizing the average atomisation energy values.
The HOMO and LUMO energies have been widely used to foretell the chemical responsiveness of chemical entities. They are called the frontier orbital energies. The HOMO energy characterizes the negatron donating nature, the LUMO characterizes the negatron accepting nature. Energy difference between HOMO and LUMO orbital is called as energy spread ( ) that is an of import stableness for constructions [ 45 ] . A big energy spread implies high kinetic stableness and low chemical responsiveness. The frontier orbital energies and the energy spreads are given in Table 2. There are qualitative chemical constructs such as electronegativity [ 46 ] and hardness [ 47 ] which are proposed by analyzing the energy spread values of molecules [ 48 ] . Using electronegativity and hardness, a step of stableness or responsiveness of organic molecules can be deduced. Within the cogency of Koopmans ‘ theorem, electronegativity and hardness are defined as and. From the values given in Table 2, the electronegativities of fluorinated pyridine isomers were calculated as follows: 4.41, 4.55, 4.68, 4.78 and 4.72 electron volt ( i.e, 1F & A ; lt ; 2F & A ; lt ; 3F & A ; lt ; 4F5F ) . In position of electronegativities, the order of isomers is about the same of energetic order, and the electronegativities of isomers increase with increasing of figure of fluor atoms in the system. On the other manus, from Table 2 the hardnesses of those molecules were obtained as 5.43, 5.53, 5.70, 5.80 and 6.14 ( i.e, 1F & A ; lt ; 2F & A ; lt ; 3F & A ; lt ; 4F & A ; lt ; 5F ) . This consequence confirms the energetic order of species of fluorinated pyridines.
The energy spread ( ) value of every single isomer is non the same of energetic order due to the differences in stabilisation of the rubric compounds. But their average values indicate the really same behaviour of the energetic order as expected. The average values increase in the undermentioned series: 1F & A ; lt ; 2F & A ; lt ; 3F & A ; lt ; 4F & A ; lt ; 5F. This supports that the HOMO-LUMO set spread becomes bigger which means that the system becomes more aromatic [ 49 ] .
The most well-known aromatic compound is benzene where there be a perfect delocalization of six ?-electrons. Therefore, cardinal permutation of an heteroatom decreases the aromaticity of the system to some extent due to the electronegativity difference between C and other atoms. But this loss of aromaticity can be gained back by permutation of one of Hs of the system by an negatively charged atom or group [ 50 ] . The strong negatively charged power of the substituent can draw the negatrons located on the heteroatom on the cardinal ring to heighten the aromaticity. Therefore, in our instance we expect that the aromaticities of fluorinated pyridines addition by increasing the figure of fluor substituent on the ring.
This subdivision is organized as follows. First, we analyze the public presentation of geometry- , magnetic- electronic- and ?-electron count-based aromaticity indices to measure the ?-electron delocalization of fluorinated pyridines. Second, we examine aromaticity of the rubric molecules harmonizing to some planetary and local forms. Finaly, we discuss the relationship between some global-local forms and the aromaticity indices.
Calculated HOMA, EN, GEO, I6, NICS ( 1 ) , , EFG ( 0 ) , EFG ( 0.5 ) , SA, pEDA and sEDA values were given in Table 3. The mean of the structural HOMA values vary in the undermentioned series: 0.936 & A ; lt ; 0.956 & A ; lt ; 0.957 & A ; lt ; 0.964 & A ; lt ; 0.967, as 5F & A ; lt ; 4F & A ; lt ; 1F & A ; lt ; 2F & A ; lt ; 3F, severally. This consequence is non compatible with the energetic order and the average values of HOMO-LUMO chitchat. Our computations indicate that the average values of both EN and GEO parts are acquiring larger. Note that, it seems that the GEO portion decreases the aromaticity while the EN portion additions. Therefore, the HOMA index can non know apart between the aromaticity of fluorinated pyridines. Harmonizing to the mean of the structural I6 values, I6 index additions in the undermentioned order: 85.906 & A ; lt ; 87.784 & A ; lt ; 89.426 & A ; lt ; 92.960 & A ; lt ; 97.376, as 1F & A ; lt ; 2F & A ; lt ; 3F & A ; lt ; 4F & A ; lt ; 5F, severally. This information is compatible with the energetic order and HOMO-LUMO chitchat. Therefore, we can reason that HOMA index is non succesful in foretelling the aromaticity of fluorinated pyridines but Bird index is, and besides as seen in this instance the larger favoritism occurs.
The mean of the magnetic NICS ( 1 ) and values increase ( perfectly ) in the undermentioned series: -10.315 ; -66.202 & A ; lt ; -10.389 ; -91.654 & A ; lt ; -10.433 ; -118.28 & A ; lt ; -10.612 ; -147.371 & A ; lt ; -10.943 ; -175.942 ; as 1F & A ; lt ; 2F & A ; lt ; 3F & A ; lt ; 4F & A ; lt ; 5F, severally. Calculated NICS and values confirm that aromaticity of fluorinated pyridines additions with every substituted fluor atom due to the disturbance of ?-electron delocalization by the substituent, and are compatible with the energetic order and the average values of HOMO-LUMO chitchat. But their highest calculated values for every single isomer do non accommodate to energetically most stable isomer in its species.
Obtained electronic EFG ( 0 ) values show that all fluorinated pyridines are aromatic, and the mean of the EFG ( 0 ) values vary in the undermentioned series: 2.543 & A ; lt ; 2.824 & A ; lt ; 3.032 & A ; lt ; 3.255 & A ; lt ; 3.399, as 1F & A ; lt ; 2F & A ; lt ; 3F & A ; lt ; 4F & A ; lt ; 5F, severally. This consequence is compatible with the energetic order and the average values of HOMO-LUMO chitchat. In contrast to magnetic-based indices, the highest EFG ( 0 ) value ( except 4F isomers ) has been obtained for energetically most stable isomer in its species. The same consequence has non been obtained for the EFG ( 0.5 ) index, the mean of the EFG ( 0.5 ) values were calculated in the undermentioned order: 0.658 & A ; lt ; 0.680 & A ; lt ; 0.686 & A ; lt ; 0.688 & A ; lt ; 0.696, as 5F & A ; lt ; 1F & A ; lt ; 4F & A ; lt ; 3F & A ; lt ; 2F, severally. The obtained consequences by utilizing two EFG indices inconsistently match with each other. Pakiari [ 37 ] has reached similar decisions for multi-fluorobenzenes by utilizing same indices.
The deliberate negatron densenesss ( ) at BCPs of each ring of fluorinated pyridines are summarized in Table S1 of Supplementary stuffs. Note that, in the AIM theory, since the negatron densenesss of the same sort of bonds are meaningfully compared with each other [ 51 ] , the negatron densenesss of four C-C BCPs are considered in the SA index computations. The mean of electronic SA values lessening in the undermentioned series: 0.0073 & A ; gt ; 0.0061 & A ; gt ; 0.0038 & A ; gt ; 0.0016 & A ; gt ; 0.0001, as 1F & A ; gt ; 2F & A ; gt ; 3F & A ; gt ; 4F & A ; gt ; 5F, severally. As seen the order is same with those in the aromaticity of fluorinated pyridines predicted by the mean I6, NICS ( 1 ) , and EFG ( 0 ) values. However, if we look at SA value of every single isomer we see that the SA values are no dependable. For illustration, the SA index predicts that the 2F3 isomer is the most aromatic compound among the fluorinated derived functions, while the other indices ( except HOMA ) do non give consistent consequences with this. This is likely since of that in all these computations merely C-C bonds are considered, but all the bonds ( C-C and C-N ) participate in electron delecolazition. Therefore it can be said that the remarks given with the average SA values are contreversial topic in footings of the truth.
To analyse ?- and ?- negatron distributions in the fluorinated pyridines we employed the ?- and ?- negatron count based aromaticity indices pEDA and sEDA. The mean of pEDA and sEDA values were calculated as: 0.074, 0.169 ; 0.151, -0.423 ; 0.230, -1.021 ; 0.308, -1.618 ; 0.389, -2.218 for 1F, 2F, 3F, 4F and 5F, severally. Harmonizing to pEDA and sEDA indices, aromaticities of fluorinated pyridines addition in the undermentioned sequnce: 1F & A ; lt ; 2F & A ; lt ; 3F & A ; lt ; 4F & A ; lt ; 5F. The pEDA and sEDA indices show the same inclination as I6, NICS ( 1 ) , , EFG ( 0 ) and SA indices. Unlike the other indices, the highest pEDA value has ever been obtained for energetically most stable isomer in its species.
Table 4 presents the quantitative description of the common correlativities between the informations of Table 3. As seen HOMA and EFG ( 0.5 ) do non correlate with other aromaticity indices as expected. This is non observed for the other aromaticity indices, i.e. , I6, NICS ( 1 ) , , EFG ( 0 ) , SA, pEDA and sEDA, which are nicely correlated with each other. Particularly, there exist the important correlativities between the pEDA/sEDA index and other indices.
Correlation between the global-local forms and the aromaticity indices
To demo the correlativities between the global-local forms and aromaticity indices the coefficients are found and given in Table 5. As presented the average HOMO-LUMO and atomisation energy values as planetary forms are good correlated to aromaticity indices – with HOMA and EFG ( 0.5 ) as an exclusion. But the better correlativity is observed between the average atomisation energy values and EFG ( 0 ) index with a correlativity coefficient of R2=0.996. So, it can be said that the EFG ( 0 ) index is more dependable than other indices. In order to verify this consequence, the correlativities between the atomisation energy ( D0 ) and the used aromaticity indices are besides investigated for every single isomer. Again looking at Table 5, the EFG ( 0 ) index correlates moderately good with the D0 steps ( R2=0.971 ; see Figure 2 ) , whereas the pEDA, , sEDA, I6, SA, HOMA and NICS ( 1 ) indices follow a poorer tendency ( R2=0.784 – 0.004 ) . Since both the consequence are same, we conclude that the EFG ( 0 ) index is more succesful and dependable than other indices.
Introduction of negatively charged groups such as halogen atoms into the pyridine ring increases its basicity [ 52 ] . On the other manus, it has been late shown that the H bond strength qualitatively parallels an addition of basicity of the proton acceptors and givers [ 53 ] . To this terminal we modeled composites between fluorinated pyridines and H2O molecule ( Fig. 3 ) . Valuess of the corrected interaction energy with BSSE ( Eint ) as planetary form at B3LYP/6-31+G ( vitamin D, P ) degree are besides reported in Table 2. Inspection of Table 2 indicates that the average interaction energy values of fluorinated pyridine – H2O composites are ordered: 5.849 & A ; lt ; 5.007 & A ; lt ; 4.380 & A ; lt ; 3.421 & A ; lt ; 2.484, as 1F & A ; lt ; 2F & A ; lt ; 3F & A ; lt ; 4F & A ; lt ; 5F, severally. This consequence is compatible with the energetic order and the average values of HOMO-LUMO chitchat. Morever, the comparision of the interaction energies and aromatic indices reveals first-class correlativities ( see Table 5 ) . These correlativities clearly demonstrate that the interaction energy plays an of import function in foretelling the aromatic character of fluorinated pyridines.
In add-on, the electric field gradient values ( EFGC-F ( 0 ) ) on the in-between points of C-F bonds and ?-electron population ( N? , amount of the s, post exchange and py natural atomic orbitals ) of N atom in the ring as local forms are applied to gauge ?-electron delecalization for the fluorinated pyridines. Note that once more, because of the larger electronegativity of the N atom, it is expected that the ?-electron population ( N? ) of the N atom will be slightly localised, lending less to the aromaticity of the ring. This decreasing of the aromaticity of the ring system has been compensated by the permutation of negatively charged atom because interpolation of an negatively charged atom into system will draw the negatrons located on the N atom of the ring, which will take to an improved aromaticity. As a consequence, in our instance we expect that the average N? values lessening with incresing of the figure of fluor atoms in the ring. But, for the average EFGC-F ( 0 ) values this state of affairs is frailty versa due to the increasing of negatron denseness of the C-F bonds. The deliberate EFGC-F ( 0 ) ( see Table S2 for EFG value of each C-F bond ) and the N? values of the fluorinated pyridines are given in Table 6. As seen from the tabular array, the average N? values of the fluorinated pyridines lessening with every fluor permutation whereas the average EFGC-F ( 0 ) values increase as explained above. Besides, the local forms are correlated really good with the used aromaticity indices except HOMA and EFG ( 0.5 ) ( see Table 5 ) . Harmonizing to these consequences, the used local forms are an effectual investigation for aromaticity of fluorinated pyridines.
To measure the electronic and aromatic belongingss of the fluorinated pyridines quatum chemical computations were applied. As a consequence of this survey we have concluded that
It has been shown that the most stable isomers in the mono- , di- , tri- , and tetrafluorinated species are 1F2, 2F4, 3F5, and 4F1 isomers, severally.
Harmonizing to the average atomisation energy values the comparative stableness order was obtained as 1F & A ; lt ; 2F & A ; lt ; 3F & A ; lt ; 4F & A ; lt ; 5F.
Increasing inclination of aromaticity was noted in the series 1F & A ; lt ; 2F & A ; lt ; 3F & A ; lt ; 4F & A ; lt ; 5F.
All studied aromaticity indices except HOMA and EFG ( 0.5 ) are succesful in foretelling the aromaticity of fluorinated pyridines. But, the comparision of the atomisation energies and used indices for every single isomer and their speices indicated that EFG ( 0 ) index is more dependable than the other indices. Besides, SA index failed when looked at SA value of every single isomer.
Merely pEDA index is succesful in happening energetically most stable isomer in its species among aromaticity indices.
Some planetary ( HOMO-LUMO spread ( ) , atomisation energy ( ) and interaction energy ( Eint ) ) and local ( EFGC-F ( 0 ) , N? ) forms are good correlated to aromaticity indices. Therefore, they can be used for assesing the aromaticity of fluorinated pyridines.
For now, there are no published informations from computational probes of electronic and aromatic belongingss of fluorinated pyridines, so our computations provide a utile reading of literature informations for similiar sorts of molecules.
Recognitions We would wish to thank Dr. Fatih Ucun from Department of Physics ( S & A ; uuml ; leyman Demirel University ) in Isparta ( Turkey ) for helpful treatments about the aromaticity computations.