Is diethyl ether polar? – (Polarity of diethyl ether)
Diethyl ether is represented by the chemical formula C4H10O. It exists as a colorless, highly flammable, sweet-smelling, volatile liquid.
Diethyl ether (molar mass = 74.12 g/mol) is commonly used as a solvent in the chemical industry, particularly useful as a fragrance enhancer and flavoring agent in perfumes and food products.
In this article, you will find the answer to an often mind-boggling question, i.e., is diethyl ether polar or non-polar?
So, let’s explore together the polarity of diethyl ether for a definitive answer.
Is diethyl ether polar or non-polar?
Diethyl ether is a polar molecule.
It consists of a polar ether (C-O-C) linkage between two ethyl (CH2CH3) groups. The three main types of covalent chemical bonds present in diethyl ether are C-C, C-H and C-O.
A C-C bond is purely non-polar as it is formed between two identical carbon atoms having zero or no electronegativity differences.
A C-H bond is very weakly polar (almost non-polar as per Pauling’s electronegativity scale), as a small electronegativity difference of 0.35 units exists between the bonded atoms.
In contrast, the C-O bonds are strongly polar as per a high electronegativity difference of 0.89 units between the covalently bonded atoms.
It is due to the asymmetric, bent shape of the molecule w.r.t the central O-atom that the strong C-O and small C-H dipole moments do not get canceled equally.
Thus, Diethyl ether is overall polar with a specific resultant dipole moment value (net µ > 0).
Name of molecule
Diethyl ether
Bond type
Polar covalent (C-O bonds)
Molecular geometry
Tetrahedral (w.r.t each C-atom)
Bent, angular or V-shaped (w.r.t the central O-atom)
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 is considered non-polar.
The following three factors mainly influence the polarity of a molecule:
Electronegativity difference between two or more covalently bonded atoms
Dipole moment
Molecular geometry or shape
Now let’s see how the above three factors contribute to making diethyl ether a polar molecule overall.
Factors affecting the polarity of diethyl ether
Electronegativity
It is defined as the ability of an elemental atom to attract a shared pair of electrons from a covalent chemical bond.
Electronegativity increases across a period in the Periodic Table while it decreases down the group.
Greater the electronegativity difference between bonded atoms in a molecule, the higher the bond polarity.
The three main elemental atoms present in a diethyl ether molecule are carbon, hydrogen and oxygen.
Carbon (C) belongs to Group IV A (or 14) of the Periodic Table of elements. Its electronic configuration is 1s2 2s2 2p2. It has a total of 4 valence electrons which means it is still deficient in 4 more electrons in order to gain a stable octet electronic configuration.
Hydrogen (H) lies at the top of the Periodic Table in Group I A (or 1). Its electronic configuration is 1s1, which implies that it lacks 1 more electron to complete its duplet.
Oxygen (O) belongs to Group VI A (or 16). Its electronic configuration is 1s2 2s2 2p4. It has a total of 6 valence electrons. It thus needs 2 more electrons in order to complete its octet.
Atom
Electronic configuration
Valence electrons
Hydrogen (1H)
1s1
1
Carbon (6C)
1s2 2s2 2p2
4
Oxygen (8O)
1s2 2s2 2p4
6
As per the Lewis dot structure of diethyl ether, it consists of 2 C-C bonds, 2 C-O bonds, and 10 C-H bonds.
All four valence electrons of each C-atom get consumed in covalent bonding; thus, there is no lone pair on any of the carbon atoms. However, the central O-atom carries 2 lone pairs of electrons.
As per Pauling’s electronegativity scale, a polar covalent bond is formed between two dissimilar atoms having an electronegativity difference between 0.4 to 1.6 units.
A C-C bond is purely non-polar as zero or no electronegativity difference is present between two identical C-atoms. Thus, the covalently-bonded electron cloud stays equally shared between the two carbon atoms.
In a C-H bond, only a small electronegativity difference of 0.35 units is present between a carbon (E.N = 2.55) and a hydrogen (E.N = 2.20) atom.
It is less than 0.4 units; therefore, the C-H bond is also considered non-polar as per Pauling’s electronegativity scale.
However, as it is formed between two dissimilar atoms, therefore a slight polarity effect may exist in the C-H bond in reality.
Contrarily, a high electronegativity difference of 0.89 units is present between a carbon and an oxygen (E.N = 3.44) atom. Thus, the C-O bonds are strongly polar.
Oxygen, being strongly electronegative, attracts not only the C-O bonded electrons but also the C-H bonded electrons towards itself.
Hence, the central O-atom obtains a partial negative charge (δ–) while the corresponding C and H-atoms obtain strong partial positive charges (δ+), as shown below.
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 charge 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 center to the center of the negative charge.
In diethyl ether, the small dipole moment of each C-H bond points from Hδ++ to Cδ+ while the strong dipole moment of both C-O bonds point from Cδ+ to Oδ–.
Molecular geometry
According to the valence shell electron pair repulsion (VSEPR) theory of chemical bonding, diethyl ether is an AX4-type molecule w.r.t each C-atom while it is an AX2E2 – type molecule w.r.t the central, more electronegative O-atom.
Thus, the shape of the molecule w.r.t each C-atom is tetrahedral while that w.r.t O-atom is bent, angular or V-shaped.
To one oxygen atom at the center (A), two bond pairs (X) are attached, i.e., two C-atoms, and it carries 2 lone pairs of electrons (E) as well. The 2 lone pairs lead to strong lone pair-lone pair and lone pair-bond pair electronic repulsions.
This strong repulsive effect distorts the shape and geometry of the molecule, consequently, diethyl ether adopts a bent shape, different from its ideal electron pair geometry, i.e., tetrahedral.
It is due to the bent shape that the small C-H and strong C-O dipole moments stay uncancelled to produce an overall polar molecule.
In turn, the charged electron cloud stays non-uniformly spread over the molecule. Hence, diethyl ether is overall polar (net µ = 1.15 D).
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), methanol (CH3OH), acetone (C3H6O), diethyl ether (C2H5)2O, etc.
Examples include oxygen (O2), nitrogen (N2), methane (CH4), n-hexane (C6H14), cyclohexane (C6H12), benzene (C6H6), ethylene glycol (C2H6O2), etc.
FAQ
Why is diethyl ether polar?
Diethyl ether is polar as it consists of a strongly polar ether (C-O-C) functional group present between two relatively non-polar alkyl chains.
Each C-O bond possesses a high dipole moment as a specific electronegativity difference of 0.89 units exists between the covalently bonded carbon and oxygen atoms.
The strong C-O dipole moments stay uncancelled due to the bent, angular or V-shape of diethyl ether w.r.t the central O-atom.
This leads to a resultant dipole moment value greater than zero and a polar ether molecule, i.e., diethyl ether.
Is hexane more polar than diethyl ether?
No. Hexane is a non-polar molecule, while diethyl ether is polar.
Diethyl ether consists of a strongly polar ether (C-O-C) functional group. The strong C-O dipole moments stay uncancelled due to the asymmetric, bent shape w.r.t the central O-atom to yield an overall polar molecule.
In contrast, both n-hexane and cyclohexane molecules possess non-polar C-C bonds and very weakly polar C-H bonds. The small C-H dipole moments get canceled equally due to the trigonal planar shape of n-hexane and cyclohexane w.r.t each C-atom.
Diethyl ether is a polar molecule while both benzene (C6H6) and tetra chloromethane (CCl4) are strictly non-polar.
Benzene (C6H6) consists of entirely non-polar C-C and C=C bonds as well as weakly polar C-H bonds, arranged hexagonally in a ring arrangement. The small C-H dipole moments get canceled equally due to the trigonal planar shape of benzene w.r.t each C-atom.
Carbon tetrachloride or tetra chloromethane (CCl4) is composed of four strongly polar C-Cl bonds having an electronegativity difference of 0.61 units between the bonded atoms.
However, the C-Cl dipole moments get canceled equally due to the tetrahedral shape of CCl4 w.r.t the central C-atom.
Diethyl ether is polar as the C-O dipole moments stay uncancelled due to the bent shape of the molecule w.r.t O-atom.
Why is benzoic acid soluble in diethyl ether?
Like dissolves like. Benzoic acid is a polar molecule containing a strongly polar carboxyl (COOH) group bonded to a non-polar phenyl ring.
The polar COOH group of benzoic acid develops strong forces of attraction with the polar ether (C-O-C) group of diethyl ether.
Contrarily, the non-polar phenyl ring develops attractive forces with the alkyl chains of diethyl ether and gets solubilized.
Which is more polar? Methanol (alcohol) or diethyl ether (an ether)?
Alcohols are generally more polar than ethers.
The hydroxyl (OH) functional group present in an alcohol such as methanol is strongly polar as a high electronegativity difference of 1.24 units exists between the covalently bonded oxygen and hydrogen atoms.
It is higher than the electronegativity difference of 0.89 units between the carbon and oxygen atoms in a C-O bond.
Greater the electronegativity difference, the higher the bond polarity.
Thus, methanol is more polar than diethyl ether as the former possesses a higher net dipole moment value.
Why is diethyl ether considered a non-polar solvent in the chemistry laboratory, even though it is a polar molecule?
Each diethyl ether molecule is polar, possessing a net dipole moment value. However, the ether is sometimes referred to as a non-polar solvent in laboratory practices as it has a small dielectric constant (4.3).
A lower dielectric constant simply means that the electrical charge present on the molecule is relatively unstable.
It is because of this reason that diethyl ether has limited water solubility (6.05 g/100 mL at r.t.p).
Summary
Diethyl ether (C2H5)2O is a polar molecule.
It consists of two ethyls (CH2CH3) groups joined together via an ether (C-O-C) linkage.
The C-C and C-H bonds present in diethyl ether are non-polar and negligibly polar, respectively.
The two C-O bonds are strongly polar as per an electronegativity difference of 0.89 units between the covalently bonded atoms.
The strong C-O dipole moments stay uncancelled due to the asymmetric, bent shape of diethyl ether w.r.t the central O-atom. Hence, diethyl ether is overall polar (net µ > 0).
References
Master Organic Chemistry. Substitution reactions by James Ashenhurst (December 6th, 2022). ‘Polar Protic? Polar Aprotic? Nonpolar? All About Solvents.’’ https://www.masterorganicchemistry.com/2012/04/27/polar-protic-polar-aprotic-nonpolar-all-about-solvents/
Encyclopedia of Toxicology (3rd Edition). F. Monticelli (2014). Elsevier. ‘Diethyl Ether’’. https://www.sciencedirect.com/science/article/pii/B9780123864543009878
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