Hydrogen bond fluorine atom

Carosati, E., Sciabola, S. and Cruciani, G. (2004) Hydrogen bonding interactions of covalently bonded fluorine atoms from crystallographic data to a new angular function in the GRID force field. Journal of Medicinal Chemistry, 47, 5114-5125. 

The number 12 in CFC-12 is based on the unique numbering system for CFC compounds. According to this system the CFC number is added to 90, and the result indicates the compounds number of carbon, hydrogen, and fluorine atoms, respectively. For example, in CFC-12 the sum is 102, so there is one carbon atom, 0 hydrogen atoms, and 2 fluorine atoms. The number of chlorine atoms in the compound can be inferred from the structure because carbon bonds to four atoms in CFC-12, there must be two chlorine atoms. 

E. Carosati, S. Sciabola, G. Cruciani, Hydrogen Bonding Interactions of Covalently Bonded Fluorine Atoms From Crystallographic Data to a New Angular Function in the GRID Force Field, J. Med. Chem. 2004, 47, 5114-5125. 

Alkyl halides are widely used as refrigerants. Unhl the late 1980s, alkyl halides called chlorofluorocarbons (CFCs) were widely used in refrigerators and air-conditioning systems. Because of their potential to damage Earth s ozone layer, CFCs have been replaced by HFCs, hydrofluorocarbons, which contain only hydrogen and fluorine atoms bonded to carbon. One of the more common HFCs is 1,1,2-trifluoroethane, also called R134a. 

It should be noted that the Av(OH) and AH values vary in opposing directions. This apparent contradiction to the Badger-Bauer rule , also found in the intermolecular association of phenols with haloalkanes , is another example of the family dependence of this rule. For 2-fluorophenol, 2,6-difluorophenol and tetrafluorohydroquinone, gas-phase electron diffraction studies indicate the existence of a weak IHB " ". The lengths of the hydrogen bonds H- -F (2.13, 2.05 and 2.02 A, respectively) are 80% shorter than the sum of the van der Waals radii of the hydrogen and fluorine atoms. 

Host commercially available fluoroelastomers consist of copolymers of vlnylidmie fluoride (VF2 ) with hexafluoropropylene (HFP), and, optionally, tetrafluoroethylene (TFE)(1,2) these highly fluorinated polymers of 62-70 wt % fluorine have remarkable resistance to flame, chemicals, solvents and oxidative attack. This stability has been attributed to the strength of the carbon-fluorine bond compared to that of the carbon-hydrogen bond, to steric hindrance due to the presence of fluorine, and to strong van der Haals forces between hydrogen and fluorine atoms present in the macromolecules. 

Where the number of hydrogen and fluorine atoms is less than that required to satisfy the four-bonds-per-carbon rule, chlorine atoms make up the sum. 

To obtain the number of hydrogen or fluorine atoms (X) with which an atom (A) will combine, one looks at compounds formed between A and X, and picks out the one in which there are no A-A bonds. If this is molecular it will have the formula AX , if non-molecular (AX )co. The valency of A is then given by n. 

Numerous ionic compounds with halogens are known but a noble gas configuration can also be achieved by the formation of a covalent bond, for example in halogen molecules, X2, and hydrogen halides, HX. When the fluorine atom acquires one additional electron the second quantum level is completed, and further gain of electrons is not energetically possible under normal circumstances, i.e... 

An sp -sp single bond where the outside atom in the bond is not a mono-coordinated terminal atom such as hydrogen or fluorine. 

Thermochemistry. Thermodynamic considerations ate of utmost importance in fluorinations. Table 1 is based on JANAF data (25) for CH, which indicate an average carbon-hydrogen bond strength of 410.0 kj/mol (98 kcal/mol) based on the atomization energy of CH. ... 

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