Is Dimethyl ether (CH3OCH3) polar or nonpolar? - Polarity of CH3OCH3
CH3OCH3 is the chemical formula for dimethyl ether. It is the simplest ether and an isomer of ethanol. It is a colorless gas that is a useful precursor to other organic compounds and an aerosol propellant with a molar mass of 46.07 g/mol.
So what is the polarity of the simplest ether (CH3OCH3)? Is dimethyl ether polar or a non-polar molecule?
Let’s find out in this article.
Is CH3OCH3 polar or non-polar?
Dimethyl ether (CH3OCH3) is a polar molecule. It consists of two methyl (CH3) groups and an oxygen (O) atom. The oxygen is kept at the central position, and both methyl groups are at the surrounding positions, one on each side, making a bent, angular, or V-shaped molecular geometry.
In CH3OCH3, two different types (C-O and C-H) of bonds are present. An electronegativity difference of 0.35 units exists between the C-H bonds, making them weakly polar, while an electronegativity difference of 0.89 units exists between highly polar C-O bonds.
Thus, C-H and C-O bonds are unequally polar in the CH3OCH3 molecule and possess a specific dipole moment value (symbol µ).
It is due to the asymmetrical bent shape of the molecule that the dipole moments of individually polar bonds are unequal and do not get canceled.
The charged electron cloud does not stay uniformly distributed in the molecule overall. As a result, the CH3OCH3 molecule is overall polar (net µ =1.30 Debye).
A molecule is polar if there is a non-uniform charge distribution present in it.
If the charge distribution gets equally balanced in different parts, then that molecule or molecular ion is considered non-polar.
The following three factors mainly influence the polarity of a molecule:
The electronegativity difference between two or more covalently bonded atoms
Dipole moment
Molecular geometry or shape
Now, let us discuss the effect of the above three factors one by one to prove that the dimethyl ether (CH3OCH3) is overall a polar molecule.
Factors affecting the polarity of CH3OCH3
Electronegativity
It is defined as the ability of an atom to attract a shared pair of electrons from a covalent chemical bond.
Electronegativity decreases down the group in the Periodic Table of elements while it increases across a period.
Greater the electronegativity difference between bonded atoms in a molecule, the higher the bond polarity.
Carbon (C) is present in Group IV A of the Periodic Table. The electronic configuration of carbon is 1s2 2s2 2p2. As per this electronic configuration, a C-atom has a total of 4 valence electrons. It is thus short of 4 more electrons that are required so that the carbon atom can achieve a complete octet electronic configuration.
Hydrogen (H) is present in Group IA of the Periodic Table. The electronic configuration of Hydrogen is 1s1. According to this electronic configuration, an H-atom has 1 electron in its only shell, and it lacks 1 more electron to complete its outer electron shell.
Conversely, oxygen (O) is present in group VI A of the Periodic Table. The electronic configuration of an oxygen atom is 1s2 2s2 2p4. As per this electronic configuration, an O-atom has a total of 6 valence electrons. It is thus short of 2 more electrons that are required so that an O-atom can achieve a complete octet electronic configuration.
Hence, in CH3OCH3, the central O-atom has two lone pairs of electrons and is bonded to two C-atoms of methyl (CH3) functional groups, each via a single covalent bond. The Lewis dot structure of CH3OCH3 displays six C-H and two C-O bonds.
2 valence electrons of the central O-atom consumed in covalent bonding out of the 6 initially available leaves behind 4 valence electrons i.e., 2 lone pairs. However, there is no lone pair of electrons on any of the C or H-atoms, respectively.
In this way, all the bonded atoms attain a completely stable octet and/or duplet electronic configuration via lone pairs and chemical bonding in CH3OCH3.
It is due to the presence of two lone pairs of electrons on the central O-atom in CH3OCH3 that the molecule experiences a distortion in its shape and geometry.
Atom
Electronic configuration
Valence electrons
Carbon (6C)
1s22s22p2
4
Hydrogen (1H)
1s1
1
Oxygen (8O)
1s2 2s2 2p4
6
The electronegativity difference between a C-atom (E. N= 2.55) and an H-atom (E. N= 2.20) in each of the three C-H bonds is 0.35 units; due to this small electronegativity difference, the C-H bonds are considered weakly polar in CH3OCH3.
Contrarily, the electronegativity difference between a C-atom (E. N= 2.55) and an O-atom (E. N= 3.44) in the C-O bond is 0.89units, and it is an extremely polar bond.
Oxygen being highly electronegative, not only attracts the C-O bonded electrons but also disturbs and attracts the shared electron cloud of each of the C-H bonds.
Thus, the oxygen atom present in the middle of the CH3OCH3 molecule gains a partial negative (Oδ-) charge due to a slight excess of electrons, while each of the C-atoms (Cδ+) and the hydrogen atoms (Hδ++) obtain partial positive charges denoting slight electron deficiency.
As a result, in the CH3OCH3, both C-H and C-O bonds are individually polar with electronegativity differences of 0.35 and 0.89 units, respectively.
Dipole Moment
Dipole moment (μ) is a vector quantity that points from the positive pole to the negative pole of a bond or a molecule.
It is mathematically calculated as a product of the magnitude of charge (Q) and charges separation (r). The dipole moment is expressed in a unit called Debye (D).
The dipole moment of a polar covalent bond conventionally points from the positive centre to the centre of the negative charge.
So in highly polar bonds of CH3OCH3, the dipole moment of polar C-O bond points from Cδ+ to Oδ while the dipole moment of weakly polar C-H bonds point from Hδ++ to Cδ+(as shown below).
Molecular geometry
According to the valence shell electron pair repulsion (VSEPR) theory of chemical bonding, CH3OCH3 is an AX2E2-type molecule. To one O-atom at the centre (A), two methyl groups or two bonded atoms (X) are directly attached (two C-atoms), and the central O-atom contains two lone pairs of electrons (E).
So, the molecular geometry or shape of CH3OCH3 is bent, angular, or V-shaped which is not identical to its ideal electron pair geometry, i.e., tetrahedral.
To minimize the repulsion and to attain stability in the distorted bent shape, the bonded atoms of the CH3OCH3 molecule possess a bond angle of ∠ (O-C-H) and ∠ (H-C-H) = 109.5° and of ∠ (C-O-C) = 111°.
Owing to the presence of two lone pairs of electrons on the central O-atom, the CH3OCH3 molecular geometry (bent, angular, or V-shaped) and electron geometry (tetrahedral) are different.
It is due to the asymmetrical bent shape of CH3OCH3 that the dipole moment of individually polar C-H and C-O bonds do not get canceled in the molecule overall.
The charged electron cloud stays non-uniformly distributed. Consequently, dimethyl ether (CH3OCH3) is overall a polar molecule (net µ = 1.30 Debye).
Difference between polar and nonpolar?
Polar molecule
Non-polar molecule
Atoms must have a difference in electronegativity
Atoms may have the same or different electronegativity values
Unequal charge distribution overall
Equal charge distribution overall
Net dipole moment greater than zero
Net dipole moment equals to zero
Examples include water (H2O), ethanol (CH3CH2OH), ammonia (NH3), sulfur dioxide (SO2), bromine trifluoride (BrF3), nitric oxide (NO), dimethyl ether (CH3OCH3), etc.
CH3OCH3 has two different types of bonds, including the C-O bond with an electronegativity difference of 0.89 units and the C-H bond with an electronegativity difference of 0.35 units between the bonded atoms.
Hence, C-O and C-H bonds are both polar and possess a specific dipole moment
It is due to the asymmetrical bent shape of CH3OCH3 w.r.t central O-atom that the charged electron cloud stays non-uniformly distributed overall, and the dipole moments of individually polar C-H and C-O bonds do not get canceled in the molecule.
Thus, Dimethyl ether (CH3OCH3) is overall a polar molecule with the net dipole moment of µ = 1.30 Debye.
Candle wax is expected to exhibit the greatest solubility in which of the following solvents? CCl4 or CH3OCH3?
Hence, the net dipole moment of each C-Cl bond is canceled out, and the vector sum of dipole moments becomes zero. Consequently, CCl4 is a non-polar molecule overall.
On the other hand, dimethyl ether (CH3OCH3) has an asymmetrical bent shape in which the dipole moment of individually polar C-O and C-H bonds are not canceled out. Hence, CH3OCH3 is a polar molecule.
Aslike dissolves like. Since candle wax is a non-polar material, it is expected to get dissolved best in a non-polar solvent i.e., CCl4.
The highly electronegative oxygen atom not only attracts the shared electron clouds of the C-O and O-H bonds but also attracts C-H bonded electrons.
The charged electron cloud stays non-uniformly distributed in the molecule overall. In conclusion, CH3OH is a polar molecule having a net dipole moment of µ = 1.69 D.
In contrast, CH3OCH3 has only two types of bonds: C-O and C-H, that possess specific dipole moments.
It is due to the asymmetrical bent shape of CH3OCH3 that the electron cloud stays non-uniformly distributed and the dipole moments of individually polar C-H and C-O bonds do not get canceled in the molecule overall.
Thus, CH3OCH3 is overall a polar molecule with a net dipole moment of µ = 1.30 D.
However, CH3OH (net µ = 1.69 D) is more polar than CH3OCH3 (net µ = 1.30 D) due to the presence of an extremely polar O-H bond having an electronegativity difference of 1.24 units between the bonded atoms, while no such bond is present in CH3OCH3.
What are the formal charges present on the bonded atoms in CH3OCH3?
Formal charge on an atom = [ valence electrons – non-bonding electrons- ½ (bonding electrons)]
For the central O-atom
Valence electrons = 6
Bonding electrons = 4
Non-bonding electrons = 4
∴ Formal charge on the central O-atom = 6 – 4 – 4/2 = 6 – 4 – 2 = 6 – 6 = 0
All atoms in the CH3OCH3 molecule including carbon, hydrogen, and oxygen obtain a formal charge equal to zero.
Hence the overall charge present on the dimethyl ether molecule is Zero.
Summary
Dimethyl ether (CH3OCH3) is a polar molecule.
It consists of six C-H and two C-O bonds.
C-H bonds are weakly polar with an electronegativity difference of 0.35 units between the bonded C-atom (E.N =2.55) and H-atom (E.N = 2.20). While the C-O bond is strongly polar with an electronegativity difference of 0.89 units between a C-atom and an O-atom (E.N = 3.44).
Dimethyl ether (CH3OCH3) has a bent, angular, or V-shaped molecular geometry with bond angles of ∠ (O-C-H) and ∠ (H-C-H) = 109.5° and of ∠ (C-O-C) = 111°.
Due to the presence of two lone pairs of electrons on the central O-atom, the CH3OCH3 molecule has an asymmetrical bent shape. The individual dipole moments do not get canceled in this asymmetrical shape of the molecule.
Thus, in CH3OCH3 there is a permanent dipole of 1.30 Debye in the molecule,so dimethyl ether is overall polar.
Vishal Goyal is the founder of Topblogtenz, a comprehensive resource for students seeking guidance and support in their chemistry studies. He holds a degree in B.Tech (Chemical Engineering) and has four years of experience as a chemistry tutor. The team at Topblogtenz includes experts like experienced researchers, professors, and educators, with the goal of making complex subjects like chemistry accessible and understandable for all. A passion for sharing knowledge and a love for chemistry and science drives the team behind the website. Let's connect through LinkedIn: https://www.linkedin.com/in/vishal-goyal-2926a122b/
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