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What is something about the bond angle of the molecule, Glucose?
Question Date: 2011-02-26
Answer 1:

Glucose occurs in both linear and cyclic forms.

In the linear form of the molecule, five of the carbons (each single bonded to four other atoms) are sp3 hybridized and one (the carbon doubled bonded to oxygen and single bonded to hydrogen) is sp2hybridized. Since the hybridization of the orbitals determines the bond angles, we know that the sp3 hybridized carbons have bond angles of ~109.5 degrees (the ideal angle for tetrahedral bonding) and sp2hybridized carbons have bond angles of ~180 degrees. I have attached astructure of glucose where I have labeled the bond angles between someof the atoms and also a 3D image of a linear glucose molecule.


Glucose can also occur in a pyranose form where it forms a six membered ring, or in a furanose form where it forms a five memberedring. When these rings are formed, the reaction destroys the double bond in the molecule so all of the atoms are sp3 hybridized. This means that they all want to have bond angles of 109.5 degrees but the strain caused by forming the ring prevents the angles from being ideal.The pyranose form behaves much like cyclohexane and exists in a"chair" conformation. Due to the way the chair conformation is puckered, it allows all of the atoms in the ring to assume bond angles very close to 109.5 degrees. The angles between the atoms in the ring will be ~ 111.4 degrees and the angles between the atoms attached to the ring will be ~107.6. I have attached a 3D image of a pyranosering.


The furanose behaves similarly to cyclopentane. When cyclopentanepuckers to achieve bond angles close to 109.5 degrees, the hydrogens start bumping into each other so to prevent this, the bond angles have to be farther from ideal. Therefore this conformation is more strained and less energetically stable. The angles between atoms in the ring will be ~104.4 degrees and the angles between atoms attached to the ring will be ~106.0 degrees.

Nelson, David L., and Michael M. Cox. "Chapter 7: Carbohydrates and Glycobiology." Lehninger Principles of Biochemistry. New York: W.H.Freeman, 2005. 241-44. Print.

Vollhardt, K. Peter C., and Neil Eric Schore. "Chapter 4: CyclicAlkanes." Organic Chemistry: Structure and Function. New York: W.H.Freeman and, 2003. 134-37. Print.
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