Is Glucose (C6H12O6) polar or non-polar? – Polarity of Glucose
Glucose, commonly known as blood sugar, is represented by the chemical formula C6H12O6. It is a carbohydrate and a monosaccharide i.e., a simple sugar unit that is the main source of energy for the human body.
In this article, we will discuss whether glucose (C6H12O6) is a polar or a non-polar molecule.
So to find the answer to this question and many other interesting facts about glucose, continue reading!
Is Glucose polar or non-polar?
Glucose (C6H12O6) is a polar molecule.
Glucose is a six-carbon compound. It is a polyhydroxy aldehyde i.e.; it consists of five hydroxyls (OH) functional groups and an aldehyde (CHO) group at carbon number 1.
The O-H bonds and a C=O bond are strongly polar, having an electronegativity difference of 1.24 units and 0.89 units between the covalently-bonded atoms, respectively.
The strong dipole moments of multiple O-H groups and a C=O group do not get canceled equally with the small dipoles of C-H bonds.
This leads to a permanent dipole moment value. Hence glucose is overall polar (net µ = 1.8 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 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 glucose is a polar molecule overall.
Factors affecting the polarity of glucose
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.
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 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 needs 2 more electrons in order to complete its octet.
The straight-chain Lewis structure of C6H12O6 is given below. It displays a six-membered carbon chain. From C2 to C4, each C-atom is bonded to two other C-atoms, 1 H-atom, and an O-H group. C1 is covalently bonded to 1 other C-atom, an H-atom, and an O-atom via a double bond.
Conversely, C6 is bonded to 2 H-atoms and an O-H group, respectively.
In this way, all the C-atoms achieve a complete octet electronic configuration via chemical bonding in C6H12O6. Thus, there is no lone pair of electrons on any C-atom; however, the O-atoms carry lone pairs.
When added to water, the straight-chain structure of glucose changes to a six-cornered cyclic arrangement (glucopyranose ring) as C1 binds to C5 via an ether/glycosidic (C-O-C) linkage.
Atom
Electronic configuration
Valence electrons
Hydrogen (1H)
1s1
1
Carbon (6C)
1s2 2s2 2p2
4
Oxygen (8O)
1s2 2s2 2p4
6
In C6H12O6, four main types of single covalent bonds are present i.e., a C-C bond, C-H bond, C=O bond and O-H bond.
A C-C bond is purely non-polar as it is formed between two identical carbon atoms having zero or no electronegativity difference between them.
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 is present between a carbon (E.N = 2.55) and a hydrogen (E.N = 2.20) atom.
Contrarily, a C=O or C-O bond is strongly polar, having an electronegativity difference of 0.89 units between a carbon and an oxygen (E.N = 3.44) atom.
Similarly, an O-H bond is extremely polar, possessing a high electronegativity difference of 1.24units between an oxygen and a hydrogen atom.
Oppositely charged poles develop in the glucose molecule as the C-atoms gain partial positive (δ+) charges while the more electronegativity O-atoms obtain partial negative (δ–) charges.
The O-atoms being strongly electronegative attracts the C-H bonded electrons in addition to attracting the C=O and O-H electron cloud. Therefore, the H-atoms gain double partial positive (δ++) charges.
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.
In C6H12O6, the dipole moment of each O-H bond points from Hδ+ to Oδ– while the dipole moment of the C=O bond points from Cδ+ to Oδ-.
At the same time, the small dipole moment of each C-H bond points from Hδ++ to Cδ+, as shown in the figure drawn below.
Molecular geometry
According to the valence shell electron pair repulsion (VSEPR) theory of chemical bonding, in the ringed arrangement, glucose is an AX4-type molecule w.r.t each C-atom.
To a carbon atom at the center (A), four bond pairs (X) are attached, and it has no lone pairs of electrons (E). Thus, the shape of glucose w.r.t each C-atom is tetrahedral.
However, the shape of the molecule w.r.t each O-atom is bent, angular or V-shaped.
Therefore, the strong O-H dipole moments do not get canceled with the dipole moment of a C=O bond.
The charged electron cloud stays asymmetrically spread over the molecule to yield an overall polar glucose molecule (net µ> 0).
The strongly polar nature of glucose (C6H12O6) is further endorsed by its high solubility in water (a polar solvent).
Like dissolves like so, polar C6H12O6 molecules develop hydrogen bonding with polar H2O molecules and get solubilized.
FAQ
Is glucose polar?
Yes, glucose (C6H12O6) is polar.
It consists of four main types of chemical covalent bonds i.e., C-C, C-H, C=O, and O-H.
C-C bonds are purely non-polar. The C-H bonds are very weakly polar.
The C=O bond is polar, having an electronegativity difference of 0.89 units between the bonded atoms.
The O-H bonds are strongly polar, having an electronegativity difference of 1.24 units between oxygen and hydrogen.
The strong O-H dipole moments stay uncancelled in the glucose molecule to yield an overall asymmetric electron cloud distribution and, thus, polar glucose (net µ = 1.8 D).
Is glucose more polar than isopropyl alcohol?
Yes, glucose (C6H12O6) is more polar than isopropyl alcohol (CH3CH(OH)CH3) as only 1 strongly polar hydroxyl (OH) functional group is present in isopropyl alcohol while 5 O-H groups are present in a glucose molecule.
Which out of the two is polar? Glucose vs. Glucosamine.
Both glucose (C6H12O6) and glucosamine (C6H13NO5) are polar molecules.
C6H12O6 consists of strongly polar C-O and O-H bonds. Contrarily, C6H13NO5 comprises polar C-N and N-H bonds in addition to the C-O and O-H bonds.
High electronegativity difference (> 0.4 units) leads to strong dipole moment values.
The dipole moments of individually polar bonds stay uncancelled to yield an overall polar glucose or glucosamine molecule with a permanent dipole moment value.
How many non-polar covalent bonds does glucose contain?
12non-polar covalent bonds are present in a glucose molecule.
Explanation:
As per Pauling’s electronegativity scale, a covalent chemical bond is formed between two dissimilar atoms having an electronegativity difference of at least 0.4 units between the bonded atoms.
As per the above definition, a C-C bond, as well as a C-H bond, is considered non-polar.
There are 5 C-C bonds and 7 C-H bonds in a glucose (C6H12O6) molecule. Thus, a total of 5 + 7 = 12 non-polar covalent bonds.
What are the formal charges present on the bonded atoms in C6H12O6?
Formal charge on an atom = [ valence electrons – non-bonding electrons- ½ (bonding electrons)]
Zero or no formal charges are present on the bonded atoms (carbon, hydrogen, and oxygen) in a glucose molecule.
Therefore, there is no overall charge present on C6H12O6. It is thus a neutral molecule.
Summary
Glucose (C6H12O6) is a polar molecule. It is a hexose sugar containing multiple hydroxyl (OH) functional groups.
Each O-H bond is strongly polar, having an electronegativity difference of 1.24 units between the bonded atoms.
Glucose also possesses a polar C-O (or C=O) bond. The C-C and C-H bonds present in C6H12O6 are non-polar and weakly polar, respectively.
The strong O-H and C-O dipole moments do not get canceled with the small C-H dipole moments.
The charged electron cloud stays non-uniformly spread; thus, glucose is a polar molecule, having a permanent dipole moment value.
Polar C6H12O6 molecules get readily solubilized in polar solvents such as water (H2O) by developing strong intermolecular forces of attraction i.e., hydrogen bonding.
References
‘Molecular structure of glucose’’. Khan Academy. Retrieved from https://wwwkhanacademy.org/science/biology/macromolecules/carbohydrates-and-sugars/v/molecular-structure-of-glucose
‘Complex biological molecules: Carbohydrates’’. Retrieved from https://sphweb.bumc.bu.edu/otlt/mph-modules/ph/ph709_basiccellbiology/ph709
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