Is Ethyl acetate polar or nonpolar? – Polarity of Ethyl acetate

Ethyl acetate is an ester represented by the chemical formula CH₃COOCH₂CH₃.

Ethyl acetate (molar mass = 88.11 g/mol) is formed by the condensation reaction of ethanol with acetic acid. It is used as a solvent in varnishes, lacquers, photographic films, etc.

Let’s find out through this article the answer to a very pertinent question that often confuses chemistry students, i.e., Is ethyl acetate (C₄H₈O₂) polar or non-polar?

Is Ethyl acetate polar or non-polar?

Ethyl acetate (CH₃COOC₂H₅) is a polar molecule.

Ethyl acetate is composed of three main types of elemental atoms, i.e., carbon (C), hydrogen (H) and oxygen (O).

A C-C bond is non-polar, a C-H bond is slightly polar, while the C-O and C=O bonds present in ethyl acetate are strongly polar in nature, owing to an electronegativity difference of 0.89 units between the covalently bonded atoms.

The strong dipole moments of C-O and C=O bonds do not get canceled with the weak dipole moments of C-H bonds in the bent shape of the molecule w.r.t each oxygen atom.

The charged electron cloud stays non-uniformly distributed and yields an overall polar molecule, i.e., ethyl acetate (net µ = 1.88 Debye).

What makes a molecule polar or non-polar?

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:

• 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 ethyl acetate is an overall polar molecule.

Factors affecting the polarity of ethyl acetate 

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 elemental atoms present in ethyl acetate are carbon (C), hydrogen (H) and oxygen (O).

Hydrogen (H) lies at the top of the Periodic Table of elements in Group I A (or 1). Its electronic configuration is 1s¹. It needs 1 more electron in order to gain a complete duplet electronic configuration.

Carbon (C) is present in Group IV A (or 14). Its electronic configuration is 1s² 2s² 2p². As per this electronic configuration, it has a total of 4 valence electrons. Each C-atom thus needs 4 more electrons in order to gain a complete octet electronic configuration.

In contrast, oxygen (O) is present in Group VI A (or 16) of the Periodic Table. Its electronic configuration is 1s² 2s² 2p⁴. It has a total of 6 valence electrons, so it requires 2 more electrons to complete its octet.

The Lewis dot structure of ethyl acetate displays 2 C-C bonds, 8 C-H bonds, 2 C-O bonds, and 1 C=O bond. There is no lone pair of electrons on any of the C-atoms in this structure. However, both O-atoms contain 2 lone pairs of electrons each.

In this way, all the C and O-atoms attain a complete octet via chemical bonding and lone pairs in ethyl acetate, while each H-atom completes its duplet.

The C-C bonds are purely non-polar as zero or no electronegativity difference is present between two identical carbon atoms. A small electronegativity difference of 0.35 units is present between carbon (E.N = 2.55) and hydrogen (E.N = 2.20) in each C-H bond.

Contrarily, a high electronegativity difference of 0.89 units is present between carbon and oxygen (E.N = 3.44) in each C-O or C=O bond present in ethyl acetate.

Oxygen, being highly electronegative, strongly attracts each C-H electron cloud in addition to attracting the C-O and C=O bonded electrons.

The O-atoms thus gain partial negative charges (δ^–) due to a slight excess of electrons, while the C and H-atoms obtain partial positive charges (δ⁺), denoting their electron deficiency, as shown below.

So both the C-O and the C=O bond is polar in ethyl acetate, while the C-H bonds are only weakly polar.

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 center to the center of the negative charge.

So in ethyl acetate, the small dipole moments of C-H bonds point from H^δ++ to C^δ+ while the strong dipole moments of C-O and C=O bonds point from C^δ+ to O^δ-.

Molecular geometry or shape

According to the valence shell electron pair repulsion (VSEPR) theory of chemical bonding, ethyl acetate is an AX₄-type molecule w.r.t each C-atom, while an AX₂E₂-type molecule w.r.t both the O-atoms.

To one O-atom at the center (A), two bond pairs (X) are attached i.e., 2 C-atoms, and it has 2 lone pairs of electrons (E). The 2 lone pairs lead to strong lone pair-lone pair and lone pair-bond pair electronic repulsions, which distorts the shape and geometry of the molecule.

It thus adopts a bent, angular or V-shape w.r.t each O-atom. In contrast, the molecular shape w.r.t the C-H bonded C-atoms is tetrahedral while that w.r.t the C=O bonded C-atom is trigonal planar.

However, it is due to the bent shape w.r.t the oxygen atom that the C-O dipole moments stay uncancelled. Also, the strong C=O dipole moment does not get canceled with the weak C-H dipole moments.

This leads to an asymmetrically distributed electronic cloud overall. Thus, ethyl acetate is a polar molecule (net > 0).

Is ethyl acetate a polar or non-polar solvent?

Ethyl acetate is essentially a polar solvent on account of the highly electronegative O-atoms and polar C-O and C=O bonds present in it.

The polar C-O or C=O bonds can develop dipole-dipole interactions with polar chemical compounds and get them solubilized.

However, ethyl acetate acts as a moderately polar solvent only and is only slightly water-soluble as it consists of weakly polar (almost non-polar as per Pauling’s electronegativity scale) C-H bonds in addition to polar C-O bonds.

Difference between polar and nonpolar?

FAQ

Summary

• Ethyl acetate (CH₃CO₂C₂H₅) is a polar molecule.
• Three main types of bonds present in ethyl acetate are C-C, C-H and C-O (or C=O) bonds.
• A C-C bond is non-polar. A C-H bond is weakly polar as an electronegativity difference of 0.35 units is present between the bonded atoms.
• A C-O bond is strongly polar owing to an electronegativity difference of 0.89 units between the bonded atoms.
• The strong C-O or C=O dipole moments do not get canceled with the weak C-H dipole moments in the bent, angular or V-shape w.r.t the C-O-C bonded oxygen atom. So, ethyl acetate is a polar molecule (net µ > 0).
• Ethyl acetate is a moderately polar solvent. It is only slightly water-soluble as ethyl acetate has a lower dielectric constant as compared to water.

References

1. National Library of Medicine. ‘Ethyl acetate. Compound Summary’’. https://pubchem.ncbi.nlm.nih.gov/compound/Ethyl-Acetate.
2. Vedantu. ‘Why is ethyl acetate insoluble in water?’’. https://www.vedantu.com/question-answer/ethyl-acetate-insoluble-in-water-class-11-chemistry-cbse-61176e1af5da6979fcbd8470.