Kendrick mass scale: Difference between revisions
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The Kendrick mass scale defines a [[units of mass|unit of mass]] '''kendrick''' ('''Ke''') which is useful in chemistry of hydrocarbons. The kendrick is close to the [[Dalton (unit)|dalton]] (=[[unified atomic mass unit]]) but it uses the group CH<sub>2</sub> as the basis of an integer mass. |
The Kendrick mass scale defines a [[units of mass|unit of mass]] '''kendrick''' ('''Ke''') which is useful in chemistry of hydrocarbons. The kendrick is close to the [[Dalton (unit)|dalton]] (=[[unified atomic mass unit]]) but it uses the group CH<sub>2</sub> as the basis of an integer mass. |
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When measuring the masses of hydrocarbon molecules in kendricks, all [[homology (chemistry)|homologous]] molecules will have the same Kendrick Mass Excess Δ''m''. |
When measuring the masses of hydrocarbon molecules in kendricks, all [[homology (chemistry)|homologous]] molecules will have the same Kendrick Mass Excess Δ''m''. |
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This unit simplifies the interpretation of a hydrocarbon [[mass spectrum]] |
This unit simplifies the interpretation of a hydrocarbon [[mass spectrum]] |
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<ref name='Kendrick 1963'> {{cite journal|title=A mass scale based on CH<sub>2</sub> = 14.0000 for high resolution mass spectrometry of organic compounds|journal=[[Anal. Chem.]]|date=1963|first=Edward|last=Kendrick|coauthors=|volume=35|issue=|pages=2146–2154|id= |url=http://pubs.acs.org/doi/abs/10.1021/ac60206a048|format=|accessdate=2010-01-25 }}</ref><ref name="pmid14730994">{{cite journal |author=Marshall AG, Rodgers RP |title=Petroleomics: the next grand challenge for chemical analysis |journal=[[Acc. Chem. Res.]] |volume=37 |issue=1 |pages=53–9 |year=2004 |month=January |pmid=14730994 |doi=10.1021/ar020177t |url=}}</ref> |
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Revision as of 08:59, 17 October 2010
The Kendrick mass scale defines a unit of mass kendrick (Ke) which is useful in chemistry of hydrocarbons. The kendrick is close to the dalton (=unified atomic mass unit) but it uses the group CH2 as the basis of an integer mass.
When measuring the masses of hydrocarbon molecules in kendricks, all homologous molecules will have the same Kendrick Mass Excess Δm. This unit simplifies the interpretation of a hydrocarbon mass spectrum [1][2] .
Definition
The Kendrick mass unit is defined as:
- m(12CH2) = 14 Ke
In words: "the group 12CH2 has a mass of 14 Ke exactly, by definition."
- 1 Ke = 14.0156/14.000 Da = 1.00111429 Da = 1.00111429 u
Kendrick Mass Excess
Kendrick Mass Excess Δm is defined as:
- Δm = m - round(m)
or more rigorously
- Δm = m - A·Ke
where:
- Δm is the Kendrick mass excess
- A is the mass number of the molecule
- Ke is the mass unit kendrick
- m is the mass of the molecule (or isotopologue) in kendricks.
- round(m) and A·Ke are the integer masses of the molecule in kendricks.
Note:
- the Kendrick mass excess Δm is defined different than the mass excess in nuclear physics
Equivalence relation
The Kendrick mass scale was introduced to find an equivalence relation for hydrocarbons. The same relation could be expressed with modular arithmetic using the modulo operation without introducing a new mass scale.
- A ~ B (mod CH2)
The above statement is read: "A is modulo CH2 equivalent to B." Or, when considering the mass of the molecules A and B:
- m(A) ~ m(B) (mod m(CH2))
"A has the same modulo CH2 mass as B."
In a computing code the Kendrick mass defect of a molecule M, Δm(M), would be expressed as the remainder r:
- Δm(M) = r = m(M) mod m(CH2)
or, if the modulo operation nor the remainder operation are defined
- Δm(M) = m(M) - m(CH2)·round(m(M)/m(CH2))
Note that:
- most programming languages implement the modulo operation with trunc or floor instead of round
- this approach with modular arithmetic works independent of the mass units (or mass scale)
- this approach is more generalized and allows for other building blocks than CH2, e.g. in polymer chemistry
History
In 1963 the chemist E. Kendrick suggested an alternative mass scale in the following publication:
Kendrick, E.: A mass scale based on CH2 = 14.0000 for high resolution mass spectrometry of organic compounds. Anal Chem. 1963;35:2146–2154.
See also
Notes
- ^ Kendrick, Edward (1963). "A mass scale based on CH2 = 14.0000 for high resolution mass spectrometry of organic compounds". Anal. Chem. 35: 2146–2154. Retrieved 2010-01-25.
{{cite journal}}: Cite has empty unknown parameter:|coauthors=(help) - ^ Marshall AG, Rodgers RP (2004). "Petroleomics: the next grand challenge for chemical analysis". Acc. Chem. Res. 37 (1): 53–9. doi:10.1021/ar020177t. PMID 14730994.
{{cite journal}}: Unknown parameter|month=ignored (help)