Synthesis, spectroscopic characterization of novel 16α-(3-acetyl phenyl amino)-3β-hydroxy pregn-5-ene-20-one, its molecular structure, NBO analysis, intramolecular interactions studied by DFT and AIM approach

Article abstract of DOI:10.1016/j.molstruc.2014.05.068

A novel compound 16α-(3-acetyl phenyl amino)-3β-hydroxy pregn-5-ene-20-one was synthesized by Michael addition reaction and characterized with the aid of ¹H, ¹³C NMR, IR, UV and mass spectrometry. The molecular geometry of synthesized compound was calculated in the ground state by density functional theory (DFT/B3LYP) using 6-31G(d,p) basis set. ¹H and ¹³C NMR chemical shifts were calculated using Gauge-Including Atomic Orbital (GIAO) approach and these values were correlated with the experimental observations. The electronic properties such as HOMO and LUMO energies were calculated using time dependent density functional theory (TD-DFT). Stability of the molecule as a result of hyperconjugative interactions and electron delocalization were analyzed using natural bond orbital (NBO) analysis. Intramolecular interactions were analyzed by AIM approach. Local reactivity descriptors were calculated to study the reactive site within the molecule.

Full text of DOI:10.1016/j.molstruc.2014.05.068

Accepted Manuscript
Synthesis, spectroscopic characterization of novel 16α-(3-acetyl phenyl ami-
no)-3β- hydroxy pregn-5-ene-20-one, its molecular structure, NBO analysis,
intramolecular interactions studied by DFT and AIM approach
Arun Sethi, Dolly Shukla, Ranvijay Pratap Singh
PII:
S0022-2860(14)00582-1
DOI:
http://dx.doi.org/10.1016/j.molstruc.2014.05.068
MOLSTR 20667
Reference:
Journal of Molecular Structure
To appear in:
Received Date:
Revised Date:
Accepted Date:
25 March 2014
26 May 2014
26 May 2014
Please cite this article as: A. Sethi, D. Shukla, R.P. Singh, Synthesis, spectroscopic characterization of novel 16α-
(3-acetyl phenyl amino)-3β- hydroxy pregn-5-ene-20-one, its molecular structure, NBO analysis, intramolecular
interactions studied by DFT and AIM approach, Journal of Molecular Structure (2014), doi: http://dx.doi.org/
10.1016/j.molstruc.2014.05.068
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Synthesis, spectroscopic characterization of novel 16α-(3-acetyl phenyl
amino)-3β- hydroxy pregn-5-ene-20-one, its molecular structure, NBO
analysis, intramolecular interactions studied by DFT and AIM approach
Arun Sethia*, Dolly Shuklaa and Ranvijay Pratap Singha
aDepartment of Chemistry, University of Lucknow, Lucknow 226007, India
ABSTRACT:
A novel compound 16α-(3-acetyl phenyl amino)-3β- hydroxy pregn-5-ene-20-one was
synthesized by Michael addition reaction and characterized with the aid of 1H, 13C-NMR, IR, UV
and Mass spectrometry. The molecular geometry of synthesized compound was calculated in the
ground state by density functional theory (DFT/B3LYP) using 6-31G (d, p) basis set. 1H and 13C-
NMR chemical shifts were calculated using Gauge-Including Atomic Orbital (GIAO) approach
and these values were correlated with the experimental observations. The electronic properties
such as HOMO and LUMO energies were calculated using time dependent density functional
theory (TD-DFT). Stability of the molecule as a result of hyperconjugative interactions and
electron delocalization were analyzed using natural bond orbital (NBO) analysis. Intramolecular
interactions were analyzed by AIM approach. Local reactivity descriptors were calculated to
study the reactive site within the molecule.
Keywords: Pregnane, Michael addition, β-amino ketones, TD-DFT, NBO, AIM approach.
* Corresponding author. Tel: +919415396239
E-mail addresses: alkaarunsethi@rediffmail.com(A.Sethi)
1. Introduction
β-amino ketones are useful synthons for the synthesis of nitrogen containing bioactive molecules
[1]. Important biological activities like antibacterial, antiviral, analgesic and antitumor properties
have been reported to be associated with molecules having nitrogen and sulfur atoms
individually or in combination [2-9]. Pregnenolone and its derivatives have been reported to
possess anti-inflammatory, anti-asthmatic, cytotoxic, anti-feedant, anti-dyslipidimic, anti-oxidant
and anti-viral properties [10-16]. Taking this into account, we planned to synthesize a novel β-
amino ketone derivative of pregnane by adopting Michael addition reaction [15, 17] scheme 1.
1

The structure of synthesized compound 3 was interpreted with the help of 1H, 13C NMR, IR, UV-
Visible spectroscopy and mass spectrometry. Geometry of compounds 1 and 3 were optimized
and vibrational frequencies of compound 3 was calculated using density functional theory (DFT)
with the help of B3LYP functional and 6-31 G (d,p) basis set. The results were compared with
the experimental observations. Further, nuclear magnetic chemical shifts were calculated with
the same functional and basis set using GIAO method and results were compared with the
experimental data. HOMO-LUMO analysis was also carried out to predict various transitions
using time dependent TD-DFT approach. AIM approach has extensively been applied to classify
and understand hydrogen bonding interactions and ellipticity in the synthesized molecule. Local
reactivity descriptors were calculated to study the reactive site within the molecule.
2. Experimental
2.1. Materials and Methods
All solvents used were of analytical grade and were purified and dried according to standard
procedures (A.I. Vogel, Practical Organic Chemistry) prior to their use. Thin layer
chromatography (TLC) was performed on Silica Gel ‘G’ (Merck, India) coated plates for
1
monitoring the progress of reaction. H nuclear magnetic resonance (NMR) was recorded on
13
Bruker DRX–300 MHz and C NMR was recorded on JOEL AL 300 FTNMR (75Mz) using
TMS as an internal reference. IR spectra were recorded on Perkin Elmer FTIR spectrometer from
4000–450 cm–1 range. The spectra were analyzed using SpectrumTM Software suite. The spectra
were measured with 4 cm-1 resolution and 1 scan co-addition. ESI–MS spectra were recorded on
Agilent 6520 Q–TOF mass spectrometer. Ultraviolet absorption spectra were obtained (in the
range of 200-450 nm) using ELICO BL-200 UV-Vis spectrophotometer equipped with a 10 mm
quartz cell in chloroform.
2.2. Synthesis of 16α-(3-acetyl phenyl amino)-3β- hydroxy pregn-5-ene-20-one
200 mg (0.636 mmol) of 3β- hydroxy pregn-5, 16-diene-20-one was dissolved in 20 mL of
freshly distilled dry acetonitrile followed by addition of 85.97 mg (0.636 mmol) of m-amino
acetophenone. The reaction mixture was refluxed for 18 hours. Ice cold solution of sodium
bicarbonate was added to the reaction mixture. The synthesized compound was extracted with
2

chloroform (3 x 15mL) and the combined organic extract was washed with water, dried over
anhydrous sodium sulphate. The organic layer was concentrated under reduced pressure and the
crude concentrated product was purified by column- chromatography using ethyl acetate: hexane
(15: 85) affording 16α-(3-acetyl phenyl amino)-3β- hydroxy pregn-5-ene-20-one as viscous.
1
Molecular formula: C29H39NO3. H NMR (300 MHz,CDCl3) δ (ppm): 7.03 (1H,t, H-68,
J=7.8Hz), 6.64(1H,d, H-67, J=6.3 Hz.), 6.56 (1H,s, H-63), 6.42 (1H, d,H-69, J=6.3Hz.),5.32
(1H,d, H-42, J=5.1 Hz), 4.41 (1H,t, H-57,J=7.5), 3.56-3.47(1H,m, H-38), 4.26 (bs, 1H, -NH),
2.44 (1H,d, H-58 ) 2.26 (3H,s, H-64,65,66), 2.16(3H,s, H -59,60,61) 1.01 (3H,s, H- 70,71,72),
13
0.72 (3H,s, H-51,52,53). C NMR (75 MHz, CDCl3) δ (ppm): 211.91 (C=O, C-20), 198.27
(C=O, C-29), 148.67 (C-23), 140.72 (C-5), 135.35(C-25), 130.55 (C-27), 121.48 (C-6), 117.27
(C-28), 113.06(C-26), 111.28 (C-24), 71.77(C-3), 69.30(C-17), 54.88(C-14), 49.90(C-9),
49.33(C-4), 45.45(C-16), 42.33(C-2), 37.29(C-1), 36.63(C-13), 35.69(C-10), 35.12(C-12),
32.82(C-7), 32.10(C-15), 31.73(C-30 &C-8), 29.90(C-21), 21.47 (C-19), 20.82 (C-11), 19.56(C-
18). ESI–MS: m/z = [M+ + Na] 472,442,422,313,274. IR νmax (in cm-1): 3384.5, 2928.10,
2852.90, 1700.21, 1660.91, 1594.01, 1489.25, 1450.79, 1354.48, 1317.59, 1292.67, 1255.91,
1071.89, 814.36, 754.97, 665.88, 500.46.
O
O
NH2
H
N
reflux
O
HO
O
HO
3
2
1
Scheme 1
2.3. Computational study
The molecular geometry optimization for compound 3 was carried out with Gaussian 03 program
1
package [18] using B3LYP functional with the 6-31G (d, p) basis set. The H and 13C-NMR
isotropic shielding of 3 was calculated with the help of GIAO method [19] using B3LYP/ 6-31G
(d, p) basis set. UV-Vis spectra, electronic transitions and electronic properties such as HOMO-
LUMO were computed with the help of time-dependant DFT (TD-DFT) method. Stability of the
3

molecules as a result of hyperconjugative interactions and electron delocalization were analyzed
using Natural Bond Orbital (NBO) analysis [20]. Presentation graphics including visualization of
the molecular structures were done with the help of Gauss View [21] and intramolecular
interactions analyzed by AIM approach [22].
3. RESULT AND DISCUSSION
3.1. Molecular structure
Optimized geometrical parameters of compounds 1 and 3 presented in Fig 1 and Fig 2 were
calculated at B3LYP/6-31G (d, p) and comparison between the two optimized structures were
also carried out and presented in Table 1. The introduction of –NH2 group of meta-amino
acetophenone at C-16 position in compound 1 showed increase in C16-C17 bond length, thereby
confirming the conversion of double bond (1.34 Ǻ) to single bond (1.57 Ǻ) in compound 3.
Bond length obtained from theoretical observations of N-C23 was found to be 1.38Ǻ, which is
almost similar to N-C bond length ˜ 1.35 Ǻ in aromatic amine while bond length between C16-N
was found to be 1.45Ǻ which is also nearly similar to C-N bond length 1.46 Ǻ in aliphatic
˜
amine.
Torsional angle between C13-C17-C20-O(C=O) in compound 1 was -178.39o whereas in
compound 3, this angle was found to be -83.51o. The change in torsional angle appears to be due
to rotation of carbonyl group, which is in plane with the five member ring in compound 1, while
in compound 3, it is inclined below the plane, and this may probably be due to introduction of m-
amino acetophenone at C-16. Bond angle between C15-C16-C-17 (112.58o) of compound 1 was
greater in comparison with that of compound 3 (105.49o) and this is due change in the
hybridization of C-16 and C17 carbons. In compound 1 the C-16 and C17 carbons were sp2
hybridized, whereas in compound 3 they were sp3 hybridized. The deviation of bond angle from
the normal 120o angle (sp2 hybridized) in case of compound 1 appears to be because C-16, C-17
double bond is in conjugation with the carbonyl group at C-20 position. Whereas in compound 3,
the deviation from the normal tetrahedral angle appears to be due to bond pair- lone pair
repulsion (lone pair of nitrogen of amino group and bond pair of C15-C16 or C16-C-17), which
resulted in the decrease in the bond angle.
4

3.2. 1H and 13C-NMR Spectroscopy
1
The H and 13C NMR chemical shift of compound 3 were calculated with gauge-including
atomic orbital (GIAO) approach using B3LYP/6-31G (d, p) basis set. The experimental and
1
13
calculated values of H and C NMR chemical shifts of the newly synthesized compound 3 are
1
given in Table 2. The correlation between the experimental and calculated H NMR chemical
shift values of these compounds are plotted in graph Fig 3. These graphs shows good correlation
between the experimental and the calculated results with the coefficient of regression (R2) being
13
in the range of 0.99013 The experimental and calculated values of C-NMR chemical shifts of
the newly synthesized compound 3 are given in Fig 4. The graphs shows good correlation
between the experimental and the calculated results with the coefficient of regression (R2) being
in the range of 0.99241.
1
The H NMR spectrum (fig 5) of compound 3 showed, one proton triplet at δ 4.41
(J= 7.5 Hz) for H-57 proton, one proton triplet at δ 7.03 (J= 7.8 Hz) for H-68, one proton doublet
at δ 6.64 (J= 6.3 Hz) for H-67, one proton singlet at δ 6.56 for H-63 and one proton doublet at δ
6.42 (J= 6.3 Hz) for H-69. The appearance of these four aromatic proton, along with the broad
singlet for the secondary amino proton at δ 4.26 as well as the position of H-57 proton in
spectrum showed that the bonding has taken place between the C-16 carbon of the pregnane and
amino group of m-amino acetophenone and not between C-16 carbon of the pregnane and carbon
of the aromatic ring. Besides this, some other characteristics peaks for pregnane moiety were
also observed in the 1H NMR spectrum. The H-42 and H-58 proton were observed as a doublet at
δ 5.32 (J= 5.1 Hz) and 2.44 (J= 6.0 Hz) respectively and four singlets of three protons each δ2.26,
2.16, 1.01, and 0.72 due to methyl groups at C-30 (H-64,65,66), C-21(H -59,60,61), C-19(H-
70,71,72) and C-18(H-51,52,53) respectively.
The 13C NMR spectrum of compound 3 in Fig 6 showed that the signal for C-16
carbon, which is directly bonded to -NH2 group was observed at δ45.45 (if this carbon was
bonded with the carbon of the aromatic ring then signal for C-16 carbon would be observed
upfield), This together with signals for carbons of the aromatic ring at δ 148.67, 135.35, 130.55,
117.27, 113.06, 111.28 for C-23, C-25, C-27, C-28 (if C-28carbon was bonded with the carbon
of C-16 of the pregnane then the signal for C-28 would be observed downfield but in compound
3 bonding has taken place between nitrogen atom of amino group and carbon of C-16, due to this
5

the signal for C-28 carbon was observed at δ 117.27), C-26, C-24 respectively and a signal for
carbonyl group at 198.27 (C-29) confirmed the introduction of m-amino acetophenone at C-16
position through the nitrogen atom of amino group. Besides this all the signals for pregnane
moiety were also observed. The carbonyl carbon present at C-20 position was observed at δ
211.91. Olefinic carbons at C-5, C-6 positions were found to be at δ 140.72 and 121.48
respectively. Carbon at C-3 position was observed at δ 71.77, downfield shifting of it is due to
presence of hydroxyl group. Three methyl signals of pregnane were observed at δ 29.90, 21.47
and 19.56 which are due to C-21, C-19 and C-18 carbons respectively.
3.3. UV-Visible Spectroscopy
The UV-Visible spectrum of compound 3 has been studied by time dependent density functional
theory (TD-DFT). The HOMO-LUMO energy gap of compound 3 has been calculated at
B3LYP/6-31G (d, p) basis set. The energy gap between the HOMO and LUMO is a critical
parameter in determining molecular electrical transport properties because it is a measure of
electron conductivity [23].The absorption wavelengths for compound 3 presented in Table 3
were observed at 356 nm, 304 nm and 256 nm. The experimental band at 356 nm is attributed to
H→L transition and the band observed at 304 nm is due to H→L+1 while the band at 256 nm is
attributed to H→L+2 transitions. The transitions in compound 3 were predicted to be due to n→
π* and π→ π* transitions. UV spectrum of compound 3 is given in Fig. 7 and orbital picture of
molecular orbitals is shown in fig 8.
3.4. NBO analysis
NBO analysis has an appealing aspect of highlighting the individual bonds and lone–pair energy
that play a vital role in the chemical processes [24-26]. It is an important tool for studying
hybridization, covalence, hydrogen–bonding and Vander Waals interactions. In other words
Natural Bond Orbital (NBO) provides supplementary structural information. Second–order
perturbation theory analysis of the Fock matrix in NBO basis for compounds 3 is presented in
Table 4. The higher value of E (2) (stabilization energy or energy of hyper conjugative
interaction) points towards the greater interaction between electron donors and electron acceptors
(i.e. the more donating tendency from electron donors to electron acceptors and the greater the
extent of conjugation in the system). Delocalization of electron density between occupied Lewis-
6

type (bonding or lone pair) NBO’s and unoccupied (antibonding) non-Lewis NBO’s correspond
to a stabilizing donor–acceptor interaction. In compound 3 some of the important π→π*
interactions viz. π (C23–C24) → π*(C28–C27)/ π*(C24–C25); π(C28–C27)→ π*(C23–C24)/
π*(C26–C25); π (C25–C26)→ π*(C23–C24)/ π*(C28–C27)/ π*(C29–O31) are responsible for
the delocalization of respective π–electrons of acetophenone ring, the molecule being stabilized
by energy in the region of 17.51~23.06 kJ/mol. Other high energy interactions involving the lone
pair of electrons with the anti-bonding π electrons corresponds to n2 (O32) → π*(C20–C17), n2
(O31) → π*(C25–C29) and n2 (O31) → π *(C29–C30) stabilizing the molecule with 19.45
kJ/mol, 19.45 kJ/mol and 20.12 kJ/mol respectively and n1 (N22) →π*(C23–C24) interaction
indicates the delocalization of lone pair of electrons on the nitrogen atom of -NH group with
anti-bonding π–electron in acetophenone ring with maximum stabilization energy in the region
of 34.27 KJ/mol.
3.5. Vibrational Assignment
The Calculated and Experimental IR spectrum of compound 3 were found in the region 450-
4000 cm-1 presented in Table 5. The calculated vibrational wavenumbers are higher than the
experimental wavenumbers due to discard of anharmonicity present in real system. Therefore,
calculated wavenumbers are scaled down by a single factor 0.9608 to compare with experimental
wavenumbers. The scaled vibrational wavenumbers helps in the assignment of vibrational modes
obtained from experimental FT-IR spectrum. The correlation graphs of the experimental and
calculated wave numbers were compared. The value of correlation co-efficient (R2= 0.9995)
shows good agreement between experimental and calculated wave numbers. The correlation
graph is presented in Fig 9.
3.5.1. C-N and N-H vibrations
In IR spectrum (Fig 10) of compound 3, two bands for C-N stretching vibration were observed,
one between aromatic carbon and nitrogen and second between aliphatic carbon and nitrogen.
Stretching vibration for N22-C23 was observed at 1317.59 cm-1, showing good agreement with
the calculated wave number at 1304 cm-1. Stretching vibration for C16-N22 observed at
1255.91cm-1, shows good agreement for calculated wave number at 1213 cm-1 [27]. Besides, two
wave number for C-N stretching vibration, N-H stretching vibration for secondary amine was
7

also observed at 3384.33 cm-1 shows that meta-amino acetophenone on introduction in
compound 1 become secondary aromatic amine in compound 3. Besides this N-H bending
vibration for secondary amine and N-H wagging vibration were observed at 1489.25 and 814.36
cm-1 showing good agreement with the calculated wave number at 1493 cm-1and 844.9 cm-1
respectively.
3.5.2. C=C vibrations
The C=C stretching vibration of olefin was observed at 1660.91 cm-1. The calculated wave
number at 1674 cm-1 assigned to the C=C stretching vibration mode of olefin present at C5-C6.
In aromatic hydrocarbon, experimental values of C=C ring stretching observed at 1594, 1450.79
cm-1[28-29] were found to be in good agreement with the calculated values at 1590 and 1402cm-1
respectively.
3.5.3. C-H vibrations
Four methyl groups are present in the molecule, out of four two methyl group present at angular
position and third is attached to the C=O of ketone, while fourth is attached to the C=O of
aromatic ketone. They are assigned as Me-18, Me-19, Me-21 and Me-30. The observe stretching
vibration for methyl group at 2928.10 cm-1 for Me-21 shows good agreement with the calculated
wave numbers at 2987 cm-1 for Me-21. The CH2 stretching vibration observed at 2852.90 cm-1
shows good agreement with the calculated wave number at 2864 cm-1. Asymmetric deformation
of Me-30 was observed at 1354 cm-1, whereas the calculated value was found to be 1339 cm-1.
The observed band at 1292.67 cm-1 was assigned to CH2 wagging and twisting corresponds to
the calculated wave number at 1289cm-1. The observed band at 754.97 and 665.88 cm-1 assigned
to aromatic C=C-H out of plane bending corresponds to the calculated wave number at 761.2 and
676.7cm-1.
3.5.4. C=O and C-O vibrations
In the molecule carbonyl groups (C=O) are present at C-20 and C-29, but in IR spectrum only
one band observed at 1700 cm-1[28-29]. The calculated wave number for C=O group at C-20 and
C=O group at C-29 showed vibrations at 1716 and 1705 cm-1 respectively. The observed at
1071.89 cm-1 assigned as C-O(C3-O39) corresponds to the calculated wave number at 1052 cm-1.
8

4. Mass spectrometry
The structure of compound 3 was further confirmed by mass spectrometry presented in Fig. 11.
Though M+ of the compound at m/z 449 was not observed, however [M+ + Na] was observed at
m/z 472. Other fragments observed are m/z 442 [M+ + Na – 2CH3], m/z 422 [M+ + Na – 2CH3 –
H2O – 2H], m/z 313 [M+– C8H9NO-H·], m/z 274[M+ + Na-CH3CO-CH2=C=O-C2H2-2C2H4-
+
CH3 ].
5. AIM approach
Geometrical as well as topological parameters are useful tool to characterize the strength of
hydrogen bond. The geometrical criteria for the existence of hydrogen bond are as follows: (i)
the distance between proton (H) and acceptor (A) should be less than the sum of the Van der
Waal’s radii of these atoms. (ii) The angle between ‘donor (D), proton (H) and acceptor (A)’
should be greater than 90◦. (iii) There should be elongation of ‘donor (D) proton (H)’ bond
length. As the above criteria were often considered insufficient, hence the existence of hydrogen
bond was supported further by Koch and Popelier criteria [30] based on ‘Atoms in Molecules’
theory (i) the existence of bond critical point for the ‘proton (H) . . . acceptor (A)’ contact as a
confirmation of the existence of hydrogen bonding interaction. (ii) The value of electron density
(ρH. . .A) should be within the range 0.002–0.040 a.u. (iii) The corresponding Laplacian 2ρ(rBCP)
should be within the range 0.024–0.139 a.u. According to Rozas et al. [31] the interactions may
be classified as follows: (i) strong H-bonds are characterized by
their covalent character is established. (ii) Medium H-bonds are characterized by
and HBCP < 0 and their partially covalent character is established. (iii) Weak H-bonds are
characterized by ρ(BCP) > 0 and HBCP > 0 and they are mainly electrostatic ( where, ρ(BCP)
and HBCP are Laplacian of electron density and total electron energy density at bond critical point
respectively).The weak interactions are characterized by ρ(BCP) > 0 and HBCP > 0 and the
ρ(BCP) < 0 and HBCP < 0 and
ρ
> 0
(BCP)
distance between interacting atoms is greater than the sum of Van der Waal’s radii of these
atoms. Molecular graph of the compound 3 using AIM program at B3LYP/6- 31G (d,p) level is
presented in Fig.12. Geometrical as well as topological parameters for bonds of interacting
atoms are given in Table 6, and on the basis of above criteria, as all
ρ(BCP) and HBCP
parameters were greater than zero, hence H70…H47, H34…H48, H72…H45, H45…H51, H50…H60,
9

H57…H69, O32…H69, are weak interactions. In this article, the Bader’s theory application was
used to estimate hydrogen bond energy (E). Espinosa proposed proportionality between
hydrogen bond energy (E) and potential energy density (VBCP): E = 1/2(VBCP) [32]. According to
AIM calculation, the total energy of intramolecular interactions was calculated as -8.74 kcal/mol.
The ellipticity (ε) at BCP is a sensitive index to monitor the π-character of bond. The ε is related
to λ1 and λ2, which correspond to the eigen values of Hessian and defined by a relationship: ε =
(λ1/ λ2) − 1. The ellipticity values for bonds C23-C24, C24-C25, C25-C26, C26-C27, C27-C28,
and C28-C23 were 0.216, 0.211, 0.197, 0.222, 0.223, and 0.211 respectively. The lower values
of ellipticity confirm that there is delocalization of electron in aromatic ring [33]. However the
higher ellipticity value for C5-C6 bond (0.372) shows electrons of this bond are not delocalized.
6. Reactivity descriptors
Local reactivity descriptors such as local softness (Sk), Fukui Function (FF) and local
electrophilicity index (ωk) [34, 35] have been used in DFT theory of chemical reactivity for
defining the reactive site within a particular molecule. Fukui function f(r) is considered as one of
the most fundamental indicator for defining the site selectivity in a given molecular species and
for soft-soft type of interactions, the preferred reactive site in a molecule is the one with
maximum values of (fk, sk, ωk) [36]. Using Hirshfeld atomic charges of neutral, cation and anion
+
-
0
+
state of initial compound 1 and 3, the condensed Fukui functions (fk , fk , fk ), local softness (sk ,
-
+
-
0
,
0) and local electrophilicity indices (ωk , ωk , ωk ) for atomic sites C-16 and C-17 were
Sk Sk
+
+
+
calculated and are listed in Table 7. In case of compound 1 the values of ƒk , sk , ωk for two
atomic sites C-16 and C-17 are 0.1831, 0.0361, 0.5177 and 0.0712, 0.0140, 0.2013 respectively.
+
+
+
Similarly for compound 3, the values of local reactivity descriptors ƒk , sk , ωk for atomic sites
C-16 and C-17 are 0.0082, 0.0016, 0.0253 and 0.0099, 0.0019, 0.0303 respectively. Maximum
+
+
+
values of all the three local reactivity descriptors (fk , sk , ωk ) in case of compound 1 indicate
that C-16 site is more prone for nucleophilic attack in comparison to C-17 atomic site.
Therefore, these local reactivity descriptors calculated in case of compound 1, confirms the
favorable site of attack at C-16 position which further leads to the formation of the compound 3.
6. Conclusion
10

A novel compound 3 synthesized in one step by adopting Michael addition reaction has
been characterized with the help of 1H, 13C-NMR, IR, UV and Mass spectrometry. Compound 3
was optimized by density functional theory (DFT) with B3LYP/6-31G basis set.1H and 13C-NMR
chemical shift were calculated with the help of gauge-including atomic orbital (GIAO) approach
showing good agreement with experimental chemical shift. The UV-Visible spectrum of
compound has been studied by time dependent density functional theory (TD-DFT) showing n→
π* and π→ π* transition in compound 3. Natural bond orbital (NBO) analysis showing π→ π*, σ
→ σ * and n→ π* hyper conjugative interactions and electron delocalization, point to the
stabilization of the molecule. Intramolecular hydrogen interaction and ellipticity studied by AIM
approach showed weak hydrogen interactions and π-character of bond in aromatic ring. The local
reactivity descriptors calculated in case of compound 1, confirms the favorable site of attack at
C-16 position which further leads to the formation of the compound 3.
Acknowledgement
The authors are grateful to the SAIF division of the Central Drug Research Institute, Lucknow,
and IIT Kanpur for providing spectroscopic data.
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13

Fig.1. Optimized geometry of Compound 3 using B3LYP/6-31G(d,p) level of theory.
14

Fig. 2. Optimized geometry of Compound 1 using B3LYP/6-31G(d,p) level of theory.
15

1
Fig. 3. Correlation graph between Experimental and Calculated H NMR chemical shift of
compound 3.
R2 = 0.9924
Fig. 4. Correlation graph between Experimental and Calculated 13C NMR chemical shift of
compound 3.
16

Fig. 5. 1H NMR spectrum of compound 3.
17

Fig. 6. 13C NMR spectrum of compound 3.
18

Fig.7. UV–Vis spectrum of compound 3.
19

Fig. 8. Molecular orbitals (HOMO, LUMO, LUMO+1) of compound 3 at B3LYP/6-31G (d, p)
level.
20

R2 = 0.9995
Fig. 9. Correlation graph between Experimental and Calculated IR wavenumbers of compound 3.
Fig. 10. IR spectrum of compound 3.
21

Fig. 11. Mass Spectrum of compound 3.
22

Fig. 12. Molecular graph of compound 3 at B3LYP/6-31G (d, p) level using AIM program: bond
critical points (small red sphere), ring critical points (small yellow sphere) and bond path (pink
lines).
23

Table 1
Comparison between optimized geometrical parameters for compound 1 and 3 using B3LYP/6-
31G (d, p).
Compound 1
Bond length(Å)
C16-C17
C5-C6
Compound 3
Bond length(Å)
C16 –C17
C5-C6
1.34
1.33
1.42
1.22
1.55
1.55
1.49
1.51
1.50
1.50
1.51
1.54
1.57
1.33
1.44
1.22
1.55
1.54
1.42
1.40
1.39
1.40
1.39
1.39
1.41
1.45
1.38
C3-O23
C3-O33
C20-O22
C10-C19
C13-C18
C17-C20
C20-C21
C6-C7
C20-O32
C10-C19
C13-C18
C29-O31
C23-C24
C24-C25
C25-C26
C26-C27
C27-C28
C28-C23
C16-N22
N22-C16
C15-C16
C4-C5
C13-C17
Bond angle(o)
O23-C3-C4
Bond angle(o)
O33-C3-C4
111.8
112.5
120.3
120.3
111.8
105.4
110.0
125.2
C15-C16-C17
C17-C20-O22
C16-C17-C20
C15-C16-C17
C15-C16-N22
C16-N22-C23
24

C4-C5-C6
120.4
107.5
C17-C20-O32
C25-C29-O31
121.4
120.9
O22-C3-C2
Torsional angle(o)
Torsional angle(o)
C1-C10-C5-
C4
46.8
C1-C10-C5-
C4
47.0
C19-C10-C5-
C6
108.4
-60.7
47.7
C19-C10-C5-
C6
108.4
-59.8
48.4
C7-C8-C9-
C11
C7-C8-C9-
C11
C14-C8-C9-
C11
C14-C8-C9-
C11
C12-C13-C14-
C15
63.8
C12-C13-C14-
C15
59.8
C17-C13-C14-
C15
-35.6
-178.3
C17-C13-C14-
C15
-47.1
-83.5
C13-C17-C20-
O22
C13-C17-C20-
O32
Table 2
The Comparison between experimental and theoretical 1H and 13C NMR chemical shifts δ (ppm)
from TMS for compound 3.
25

Atom no.
H68 (t)
Experimental Calculated 1H Atom no.
Experimental Calculated
1H NMR
NMR
13C NMR
13C NMR
7.03 (J= 7.8
Hz)
7.15
C20
C29
211.91
206.32
H67 (d)
6.64 (J= 6.3
Hz)
7.02
198.27
192.08
H63 (s)
H69 (d)
6.56
7.25
6.57
C23
C5
148.67
140.72
143.59
141.72
6.42 (J= 6.3
Hz)
H42 (d)
H57 (t)
5.32 (J= 5.1
Hz)
5.48
4.64
C25
C27
135.35
130.55
135.04
127.70
4.41 (J= 7.5
Hz)
H38 (m)
H58(d)
3.56
3.71
2.21
C6
121.48
117.27
122.60
114.42
2.44 (J= 6.0
Hz)
C28
H-64,65,66
(s)
2.26
2.16
1.01
0.72
2.29
1.90
1.09
0.79
C26
C24
C3
113.06
111.28
71.77
115.82
113.06
74.50
H -59,60,61
(s)
H- 70,71,72
(s)
H-51,52,53
(s)
C17
69.30
76.50
C14
C9
54.88
49.90
49.33
45.45
60.12
55.10
49.03
59.56
C4
C16
26

C2
42.33
37.29
35.69
35.12
32.82
31.73
29.90
21.97
20.82
19.56
34.32
42.58
45.21
44.48
37.61
29.52
35.25
24.17
27.10
19.64
C1
C10
C12
C7
C30 &C8
C21
C19
C11
C18
Table 3
Electronic transitions (calculated and experimental) for compound 3.
Compounds Molecular E
Calculated Assignments Oscillatory Observed
orbitals
(eV) (λmax strength (f) (λmax
)
)
1.
2.
3.
H→ L
3.55 348
4.00 309
5.40 229
n → π*
n → π*
π → π*
0.0290
0.0447
0.4762
356
304
256
H→L+1
H→L+2
Table 4
27

Second order perturbation theory analysis of Fock Matrix in NBO Basis of compound 3.
Donor
(I)
Type of Occupancy Acceptor Type of Occupancy E2
E (j)-
F (i , j)
(a.u)c
band
(J)
band
π*
π*
π*
π*
π*
π*
π*
π*
π*
π*
π*
(kJ/mol)a E(i )
(a.u)b
C23–
C24
π
π
π
π
n
n
1.608
1.608
1.689
1.689
1.889
1.891
1.891
1.646
1.646
1.646
1.780
1.978
1.967
C28–
C27
0.3433
0.4158
0.3835
0.4158
0.0641
0.0663
0.0522
0.3835
0.3433
0.1304
0.4158
0.0372
0.0972
17.78
23.06
20.31
17.51
19.45
19.45
20.12
18.32
22.20
18.20
34.27
6.84
0.28
0.28
0.28
0.28
0.66
0.69
0.64
0.28
0.28
0.27
0.29
0.91
0.53
0.064
0.072
0.069
0.065
0.102
0.105
0.103
0.064
0.070
0.066
0.093
0.071
0.052
C28–
C27
C24–
C25
O32
C23–
C24
O31
C26–
C25
C25–
C26
C20–
C17
N22
C25–
C29
C6-H42 n
C29–
C30
C21-
H61
π
π
C23–
C24
C6-C7
C28–
C27
C7-H43 π
C29–
O31
C14-
H54
n
C23–
C24
C18-
H51
π
C5-C10 π*
C2-H37 π
O32-
C20
π*
6.34
28

C4-H40 σ
1.980
1.970
C5-C4
C6-C5
σ*
0.0234
0.0754
4.13
4.30
1.04
0.56
0.059
0.044
C24-
H63
σ
σ
σ
π *
1.968
1.987
C13-
C18
σ*
σ*
0.0242
0.0309
3.88
3.03
0.85
0.84
0.051
0.045
C13-
C17
σ
σ
σ
1.978
1.980
1.972
C10-C1 σ*
C5-C10 σ*
0.0286
0.0372
0.0252
3.72
4.17
3.64
0.84
0.90
1.16
0.050
0.055
N22-
C23
σ*
0.058
a Energy of hyper conjugative interactions.
b Energy difference between donor and acceptor i and j NBO orbitals.
c Fock matrix element between i and j NBO orbitals.
Table 5
Experimental and calculated (selected) vibrational wavenumbers of monomer using B3LYP/6-
31G (d,p) and their assignments for compound 3.
Wav
enu
mbe
r un
scal
ed
Waven
umber
Exp.
Wavenum
bers
Assignment
scaled
3660
380
9
3100-3610
Stretching vibration of
H39O33
29