Bjerrum defect

From Wikipedia, the free encyclopedia
Jump to: navigation, search

A Bjerrum defect is a crystallographic defect which is specific to ice, and which is partly responsible for the electrical properties of ice.[1] It was first proposed by Niels Bjerrum in 1952 in order to explain the electrical polarization of ice in an electric field.[2] A hydrogen bond normally has one proton, but a hydrogen bond with a Bjerrum defect will have either two protons (D defect) or no proton (L defect). The unfavorable defect strain is resolved when a water molecule pivots about an oxygen atom to produce hydrogen bonds with single protons. Dislocations of ice Ih along a slip plane create pairs of Bjerrum defects, one D defect and one L defect.[3]

Nonpolar molecules such as methane can form clathrate hydrates with water, especially under high pressure. Although there is no hydrogen bonding of water molecules when methane is the guest molecule of the clathrate, guest-host hydrogen bonding often forms with guest molecules in clathrates of many larger organic molecules, such as pinacolone and tetrahydrofuran. In such cases the guest-host hydrogen bonds result in the formation of L-type Bjerrum defect in the clathrate lattice.[4] Oxygen atoms (in alcohol or carbonyl functional groups) and nitrogen atoms (in amine functional groups) in the guest molecules lead to transient hydrogen bonds and misoriented water molecules in the hydrate lattice.[5]

See also[edit]

References[edit]

  1. ^ David E. Stillman and Robert E. Grimm (2008). "ELECTRICAL PROPERTIES OF ICE AND IMPLICATIONS FOR SOLAR SYSTEM EXPLORATION." (PDF). XXXIX. Lunar and Planetary Science. Retrieved 2010-09-09. 
  2. ^ Bjerrum, N. (11 April 1952). "Structure and Properties of Ice". Science 115 (2989): 385–390. Bibcode:1952Sci...115..385B. doi:10.1126/science.115.2989.385. 
  3. ^ Head, School of Earth Sciences (March 15, 2004). "Dislocations". School of Earth Sciences - The University of Melbourne - Australia. Retrieved 2010-09-09. 
  4. ^ Alavi S, Susilo R, Ripmeester JA (2009). "Linking microscopic guest properties to macroscopic observables in clathrate hydrates: guest-host hydrogen bonding" (PDF). Journal of Chemical Physics 130 (17): 174501. Bibcode:2009JChPh.130q4501A. doi:10.1063/1.3124187. PMID 19425784. 
  5. ^ Alavi S, Udachin K, Ripmeester JA (2010). "Effect of guest-host hydrogen bonding on the structures and properties of clathrate hydrates". Chemistry: A European Journal 16 (3): 1017–1025. doi:10.1002/chem.200902351. PMID 19946907.