Chemical Sciences: A Manual for CSIR-UGC National Eligibility Test for Lectureship and JRF/Kendrick mass

The Kendrick mass is a mass obtained by scaling the atomic mass unit (u), or dalton (Da) to simplify the display of peak patterns in hydrocarbon mass spectra.[1][2]

Definition edit

The Kendrick mass unit is defined as [3]

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 defect edit

When expressing the masses of hydrocarbon molecules in Kendrick mass, all homologous molecules will have the same mass defect Δm defined as:[4]

Δm = m - round(m)

or more rigorously

Δm = m - A·Ke


  • Δm is the Kendrick mass defect
  • A is the mass number of the molecule
  • m is the mass of the molecule (or isotopologue) which is also referred to as exact mass
  • round(m) and A·Ke are the integer masses of the molecule

Equivalence relation edit

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
  • the Kendrick mass defect Δm is defined different than the mass defect in nuclear physics

Notes edit

  1. 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)
  2. 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)
  4. Hughey CA, Hendrickson CL, Rodgers RP, Marshall AG, Qian K (2001). "Kendrick mass defect spectrum: a compact visual analysis for ultrahigh-resolution broadband mass spectra". Anal. Chem. 73 (19): 4676–81. PMID 11605846. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)