Is Sugar (C12H22O11) polar or nonpolar? – (Polarity of sugar)

The term sugar is generic. In our everyday lives, we refer to sugar as the white-colored, sweet-tasting crystals that we add to our tea, coffee, and daily food items.

For a chemist, sugar refers to carbohydrates containing multiple hydroxyls (OH) functional groups. These include monosaccharides (simple sugars) and polysaccharides (complex sugar).

The most commonly used Table sugar is a disaccharide i.e., sucrose.

So in this article, we will discuss whether sucrose (table sugar) is polar or non-polar.

Is sugar polar or non-polar?

All types of sugar, including sucrose, are polar in nature.

The polarity of a sugar molecule is accredited to the presence of strongly polar hydroxyl (OH) functional groups as well as the presence of a polar glycosidic (C-O-C) linkage in it.

Each O-H bond is polar as an electronegativity difference of 1.24 units exists between the covalently bonded oxygen and hydrogen atoms.

Conversely, a C-O bond is polar as an electronegativity difference of 0.89 units exists between the bonded carbon and oxygen atoms.

The dipole moments of individually polar bonds do not get canceled in the overall molecular shape to yield a polar sugar molecule with a permanent dipole moment (net µ = 2.35 Debye).

Name of the substance	Sugar
Chemical composition	Disaccharides composed of glucose and fructose
Name of the molecule	Sucrose  (C12H22O11)
Bond type	Polar covalent
Molecular geometry	Asymmetrical bent shape w.r.t each O-atom
Polar or non-polar?	Polar
Net dipole moment	2.35 D

Let us discuss the chemical composition of sugar in detail so that we can better understand its polar nature.

What is the chemical composition of sugar (sucrose)?

Sucrose is a disaccharide which implies that it is composed of two monosaccharides (simple sugars).

A condensation reaction takes place between a glucose molecule and a fructose molecule to prepare a sucrose molecule by the loss of water (H₂O).

Both the constituent monosaccharides consist of 6 carbon (C) atoms and 5 hydroxyls (OH) functional groups each. However, glucose is an aldose sugar containing an aldehyde (CHO) functional at the terminal (¹C). Contrarily, fructose is a ketose sugar possessing a C=O group at ²C.

In the solution form, the straight-chain structures of glucose and fructose adopt cyclic forms (as shown below).

An H-atom is removed from the OH at ¹C of alpha-D-glucose, while an OH group is removed from ²C of beta-D-fructose to yield a sucrose (C₁₂H₂₂O₁₁) molecule.

The ether (C-O-C) linkage formed as a result of this dehydration is known as a 1,2-glycosidic bond.

Sucrose also adopts a cyclic structure in solution form. It consists of a total of 12 C-atoms, 8 OH bonds, and 6 C-O bonds, respectively.

Factors affecting the polarity of sugar (sucrose)

Electronegativity

Electronegativity is defined as the ability of an elemental atom to attract a shared pair of electrons from a covalent chemical bond.

The greater the electronegativity difference between bonded atoms in a molecule, the higher the bond polarity.

There are four main types of covalent chemical bonds present in a sugar i.e., a C-C bond, a C-H bond, a C-O bond and an O-H bond.

Atom	Electronic configuration	Valence electrons
Hydrogen (1H)	1s1	1
Carbon (6C)	1s2 2s2 2p2	4
Oxygen (8O)	1s2 2s2 2p4	6

A C-C bond is purely non-covalent as zero electronegativity differences exist between identical carbon atoms.

A C-H bond is very weakly polar (almost non-polar as per Pauling’s electronegativity scale) as only an electronegativity difference of 0.35 units exists between a carbon (E.N = 2.55) and a hydrogen (E.N = 2.20) atom.

In contrast, a C-O is strongly polar as a high electronegativity difference of 0.89 units exists between a carbon and an oxygen (E.N = 3.44) atom.

Similarly, an even higher electronegativity difference of 1.24 units exists between an oxygen and a hydrogen atom, so an O-H bond is extremely polar.

There are multiple O-H groups present in sugar, so the highly electronegative O-atom of each of the O-H and C-O groups gain a partial negative charge (δ^–) while the C-atoms and H-atoms obtain partial positive (δ⁺ and δ⁺⁺) charges respectively.

Dipole moments

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.

So in a sugar molecule, the dipole moment of each O-H bond points from H^δ+ to O^δ–, while the C-O dipole moments in the glycosidic linkage point from C^δ+ to O^δ– as shown below.

Shape of the molecule

A sugar (sucrose) molecule possesses a bent, angular, or V-shape w.r.t the O-atom in the glycosidic linkage and O-atoms in each of the O-H bonds.

The strongly polar O-H groups stay exposed out of the sucrose ring. The charged electron cloud stays non-uniformly distributed in this asymmetric ringed molecular arrangement and shape.

The O-H and C-O dipole moments do not get canceled equally. Consequently, a sugar (C₁₂H₂₂O₁₁) molecule is overall polar (net µ > 0).

Polar sugar molecules can get readily dissolved in polar solvents such as water by developing strong intermolecular forces of attraction i.e., hydrogen bonding, as shown in the figure drawn below.

Also, check

• Is Soap polar or nonpolar?
• Is Vinegar polar or nonpolar?
• How to identify polar and nonpolar molecules?
• Is Water (H₂O) polar or nonpolar?

FAQ

Is sugar polar or non-polar?

Sugars such as sucrose (table sugar) are polar in nature. Chemically, sugars are carbohydrates, more specifically, polyhydroxy compounds of aldehyde and ketones. The polarity of a sugar molecule is accredited to the presence of strongly polar O-H and C-O bonds in it. Oppositely charged poles develop in a sugar molecule. The charged electron cloud stays non-uniformly distributed; thus, a sugar molecule is polar (net µ > 0).

Are simple sugars polar?

Monosaccharides, comprised of a single sugar unit such as glucose (C6H12O6), are also polar molecules based on the multiple polar hydroxyls (O-H) functional groups in them.

Is sugar polar or non-polar in water?

Like dissolves like. Thus, sugars possessing a polar character in water readily interact with polar H2O molecules and get dissolved. The partial positive end (Hδ+) of an O-H group develops strong Van der Waal’s forces of attraction (hydrogen bonding) with the partial negative end (Oδ-) of a water molecule and vice versa.

Are sugar and salts polar?

Yes, both sugar and salt are polar molecules. Table sugar (sucrose, C12H22O11) is polar owing to the presence of polar O-H and C-O covalent bonds in it. Conversely, table salt (sodium chloride, NaCl) is a polar ionic compound due to the presence of extremely polar Na+Cl– unit cells held together by strong electrostatic forces of attraction. However, NaCl is more polar than C12H22O11 because a higher electronegativity difference of 2.23 units exists between an electropositive Na (E.N = 0.93) atom and a Cl-atom (E.N = 3.16), as compared to the electronegativity differences of 1.24 units and 0.89 units between O-H and C-O bonded atoms respectively.

Is sugar hydrophobic or hydrophilic?

Sugar molecules are hydrophilic (water-loving) substances as they can easily develop an attractive force with polar water molecules and get dissolved.

Is an aqueous solution of sugar a good electrolyte?

No. Covalently bonded sugar molecules dissolve in water via hydrogen bonding. There is no ionic dissociation. No ions are produced to carry an electric current; thus, an aqueous sugar solution is not a good electrolyte.

Summary

• Sugar is polar in nature.
• Table sugar, sucrose is a disaccharide composed of glucose and fructose.
• Sucrose consists of multiple hydroxyls (OH) functional groups and a glycosidic linkage (C-O-C) in a ring arrangement.
• Each O-H and C-O bond is strongly polar owing to the electronegativity differences of 1.24 units and 0.89 units between the covalently bonded atoms, respectively.
• The dipole moments of individually polar bonds do not get canceled in the asymmetric ring arrangement (bent shape as per each of the C-O-C and O-H bonded oxygen atoms); thus, sugar is polar (resultant µ > 0).

Reference

1. ‘’Why does water dissolve sugar?’’ Retrieved from https://www.middleschoolchemistry.com/lessonplans/chapter 5/lesson 4.
2. ‘Sugar vs Sugars. ‘’Retrieved from https://www.sugar.org/sugar/sugars.
3. ‘Is sugar a polar molecule?’’ (2017, Feb 17^th). Retrieved from https://socratic.org/questions/57a8ca6311ef6b377cfe42fe