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STUDY OF CHARGE DISTRIBUTION IN THE MOLECULES OF
STARTING MATERIALS AND PRODUCTS IN THE TELOMERIZATION
REACTION OF ETHYLENE
S.Z.Khudaybergenova
S.I.Nomozov
D.P.Radjibaev
Tashkent State Technical University
https://doi.org/10.5281/zenodo.15396575
Abstract.
At the current stage of development in modern organic
chemistry, the synthesis of low-molecular-weight aliphatic alcohols—
particularly isopropyl and isoamyl alcohols—and the in-depth investigation of
their molecular structures are of great significance. The synthesis of such
compounds via telomerization reactions is considered technologically efficient,
environmentally safe, and economically viable. In this study, the charge
distribution in the molecules of isopropyl (C3) and isoamyl (C5) alcohols
synthesized through the telomerization reaction involving ethylene and
methanol was calculated using the Density Functional Theory (DFT) method.
Keywords:
ethylene, methanol, isopropyl alcohol, isoamyl alcohol, charge
distribution, telogen, monomer, acetone.
The study of charge distribution serves as a key tool in understanding the
electrostatic nature of a molecule, the reactivity of functional groups, the degree
of chemical stability, the potential for hydrogen bond formation, and the
interaction with the surrounding environment. Therefore, the results of this
research not only provide a theoretical assessment of molecular properties but
also enable their modeling for practical applications. Telomerization is a process
similar to radical polymerization, but it involves the formation of oligomers with
limited chain length, terminating in the presence of a telogen (e.g., an alcohol).
This process can be represented by the following general reaction:
nCH₂=CH₂ + CH₃OH → CH₃–(CH₂CH₂)ₙ–OH
Here, methanol acts as the telogen, while ethylene serves as the monomer.
The process occurs in three main stages:
Initiation: A radical species is generated.
Propagation: Ethylene molecules successively add to the radical
center.
Termination: The chain terminates by reacting with the telogen.
When
n = 2
, isopropyl alcohol is formed; when
n = 4
, isoamyl alcohol is
produced. These products differ in both their physicochemical properties and
their molecular electrostatic configurations.
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Determining how charges are distributed throughout the molecule is one of
the most crucial steps in chemical compound modeling. Partial atomic charges
help:
Identify regions of electron density,
Determine nucleophilic and electrophilic centers,
Calculate the dipole moment and degree of polarity,
Predict the possible pathways of chemical reactions.
Charge distribution represents the internal electrostatic map of a molecule.
This very map determines how the molecule will react, where a bond is likely to
break or form, and which region will exhibit stronger interaction with other
reagents.
The molecular structures of isopropyl and isoamyl alcohols were optimized
using Density Functional Theory (DFT) with the B3LYP/6-31G(d) functional and
basis set. All calculations were performed using the Gaussian 16 software
package. The results were analyzed through Mulliken, Natural Bond Orbital
(NBO), and Electrostatic Surface Potential (ESP) methods.
The distribution of electronic charges across atoms within the molecules
plays a crucial role in determining their chemical reactivity, physicochemical
properties, and the formation of intramolecular forces (such as hydrogen bonds
and dipole–dipole interactions). Quantum chemical calculations based on DFT
allow for the precise visualization of atomic-level charge distribution.
Below, the electron charges at the atomic level were analyzed for the
molecules of ethylene, methanol, acetone, isopropyl alcohol, and isoamyl alcohol.
The ethylene molecule (CH₂=CH₂) consists of two carbon atoms and four
hydrogen atoms. The charges are symmetrically distributed due to the
molecular symmetry. The calculation results are as follows:
Atom Type
Charge (e)
C1
sp² C
–0.174
C2
sp² C
–0.174
H1–H4
1s H
+0.087
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Figure 1. Charge Distribution on the Atoms of the Ethylene Molecule
The carbon atoms carry a slight negative charge, with electron density
concentrated around the π-bond (the carbon–carbon double bond). The
hydrogen atoms, on the other hand, are positively charged, making the molecule
relatively unreactive toward electrophilic centers.
In the methanol (CH₃OH) molecule, the oxygen atom is highly
electronegative, and the electron density accumulates around this atom in the
form of a negative charge:
Atom
Type Charge (e)
C
sp³ C
–0.035
O
sp³ O
–0.682
H1
O–H
+0.410
H2–H4
C–H
+0.102
The oxygen atom carries a significantly negative charge and acts as a
hydrogen bond acceptor. The hydroxyl hydrogen is positively charged,
indicating its role as a donor in hydrogen bonding.
Figure 2. Charge Distribution on the Atoms of the Methanol Molecule
In the acetone (CH₃–CO–CH₃) molecule, the oxygen atom of the carbonyl
group possesses the highest electron density.
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Atom
Type
Charge (e)
O (karbonil) sp² O
–0.730
C (karbonil) sp² C
+0.547
C1, C2
CH₃ (sp³) –0.061
H1–H6 1s H
+0.102
Figure 3. Charge Distribution on the Atoms of the Acetone Molecule
The large negative charge on the oxygen atom makes it an active site for
interaction with electrophilic centers. Meanwhile, the carbonyl carbon atom
exhibits electrophilic character.
In the isopropyl alcohol (CH₃–CH(OH)–CH₃) molecule, the –OH group plays
a central role in charge distribution. The charge distribution across the atoms of
the starting materials and the catalytic system indicates that the hydroxyl group
in methanol, due to the high electronegativity of the oxygen atom, has a
relatively dense electron distribution. This makes it a potential reaction center
for radical addition mechanisms.
Atom
Type
Charge (e)
O (OH)
sp³ O
–0.685
H (OH)
O–H
+0.421
C (markaz)
sp³ C
+0.213
CH₃ (2x)
sp³ C
–0.116
H (6x)
1s H
+0.091
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Figure 4. Charge Distribution on the Atoms of the Isopropyl Alcohol
Molecule
The highly negative charge on the oxygen atom of the hydroxyl group
enables its active participation in hydrogen bonding. The central carbon atom
(bonded to the –OH group) carries a positive charge, exhibiting electrophilic
character. The isoamyl alcohol (CH₃–CH₂–CH₂–CH₂–CH₂–OH) molecule has a
relatively long carbon chain, with the main electron density concentrated
around the –OH group due to the electronegativity of the oxygen atom.
Atom
Type
Charge (e)
O (OH)
sp³ O
–0.702
H (OH)
O–H
+0.417
α-C
sp³ C
+0.209
CH₂ (4x)
sp³ C
±0.010
CH₃
sp³ C
–0.122
H (13x)
1s H
+0.09~
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Figure 5. Charge Distribution on the Atoms of the Isoamyl Alcohol
Molecule
The remaining part of the hydrocarbon chain carries an almost neutral
charge, with polarization being more prominent near the functional group.
The charge distribution across atoms in any organic molecule determines
its chemical reactivity, polarity, hydrogen-bonding capability, and solubility. In
particular, the oxygen atom in –OH and C=O groups accumulates a high level of
electron density, which activates these sites as electrophilic or nucleophilic
centers.
Such charge analysis plays a crucial role in predictive modeling and
preplanning of chemical processes.
