Molar mass
Molar mass, exact mass and elemental composition for any formula, compound or SMILES, with the isotope pattern, HRMS adducts and an elemental analysis check.
Formula or compound
Molar mass
C18H36O
Molecular formula
- Rings plus double bonds
- 1
Details
- Monoisotopic mass
- 268.276616 Da
- Average mass, unrounded
- 268.485000 g/molShown above to 3 decimals, the precision of the least precise standard atomic weight in the formula.
- Mass defect
- 0.2766 Da
- Atoms
- 55
Isotope pattern
M · C18H36O · most intense peak 268.2766
| Ion | Formula | m/z | |
|---|---|---|---|
| C18H36O | 268.2766 | ||
| C18H37O+ | 269.2839 | ||
| C18H36NaO+ | 291.2658 | ||
| C18H36KO+ | 307.2398 | ||
| C18H40NO+ | 286.3104 | ||
| C18H38O2+ | 135.1456 | ||
| C18H36O+ | 268.2761 | ||
| C18H35O− | 267.2693 | ||
| C18H36ClO− | 303.2460 |
Peak list
| Mass (Da) | Relative intensity | Abundance |
|---|---|---|
| 268.27662 | 100.00 % | 81.8558 % |
| 269.28003 | 19.92 % | 16.3060 % |
| 270.28320 | 2.08 % | 1.7061 % |
| 271.28619 | 0.152 % | 0.1247 % |
Elemental composition
| Element | Atoms | Mass (g/mol) | Mass % |
|---|---|---|---|
| C Carbon | 18 | 216.198 | 80.53 |
| H Hydrogen | 36 | 36.288 | 13.52 |
| O Oxygen | 1 | 15.999 | 5.96 |
Elemental analysis
| Element | Calcd (%) | Found (%) | Δ |
|---|---|---|---|
| C | 80.53 | — | — |
| H | 13.52 | — | — |
Anal. Calcd for C18H36O: C, 80.53; H, 13.52.How the masses are calculated
The molar mass sums the IUPAC standard atomic weights, using the conventional value for elements whose weight is given as an interval (hydrogen 1.008, carbon 12.011, sulfur 32.06). It is shown to the number of decimals of the least precise atomic weight in the formula, so CuSO4·5H2O gets two decimals because of sulfur; the unrounded value is under Details.
The monoisotopic mass uses the mass of the most abundant isotope of every element, the nominal mass its mass number. Labelled atoms, written [13C], D or T, count with their own nuclide mass and are taken as fully enriched. For an ion, one electron mass, 0.000 548 579 909 u, is subtracted per positive charge and added per negative charge.
How the isotope pattern is computed
Every element's natural isotope distribution is raised to its atom count by repeated squaring, and the element distributions are then convolved with each other. In centroid mode the isotopologues are grouped by nominal mass and each group is reported at its intensity-weighted mean m/z, which is what a mass spectrometer at ordinary resolution shows; this is exact apart from dropping contributions below 10−12 of the largest. Fine structure keeps isotopologues apart, merges those closer than 0.1 mDa and drops those below 10−8 of the largest, which resolves, for example, 34S from 13C2.
Adduct m/z values follow m/z = (M + adduct − z·me) / |z|. The copy button gives the line in the form the ACS journals print, for example “[M + H]+ Calcd for C8H11N4O2 195.0877”. The ACS guidelines ask that found and calculated m/z agree within 0.003 m/z units, the limit the found m/z check uses.
Elemental analysis
Calculated percentages are mass fractions from the standard atomic weights. Journals ask for found values within ±0.4 % (absolute) of the calculated ones. If a sample holds solvent, enter it as a solvate, for example 0.5 × H2O, and the calculated values are for C8H10N4O2·0.5H2O.
Sources
Standard atomic weights: IUPAC Commission on Isotopic Abundances and Atomic Weights, “Standard atomic weights of the elements 2021”, Pure Appl. Chem. 94, 573 (2022). Isotope masses and natural abundances: NIST, Atomic Weights and Isotopic Compositions for All Elements (Standard Reference Database 144). Electron mass: CODATA 2018, Rev. Mod. Phys. 93, 025010 (2021). Reporting criteria: ACS Author Guidelines for The Journal of Organic Chemistry and Organic Letters.