Monodeuterated methane

Names
IUPAC name (2H1)methane
Other names Methane-d1 Methyl deuteride Monodeuterated methane Deuteriomethane[1]
Identifiers
CAS Number	676-49-3
3D model (JSmol)	Interactive image
Abbreviations	MeD
ChemSpider	12148
EC Number	694-721-3
PubChem CID	12669
InChI InChI=1S/CH4/h1H4/i1D Key: VNWKTOKETHGBQD-MICDWDOJSA-N
SMILES [2H]C
Properties
Chemical formula	CH3D
Molar mass	17.049 g·mol-1[2]
Density	0.76 kg/m3 (at 0 °C) 0.7 kg/m3 (at 25 °C)
Melting point	−182.6[3] °C (−296.7 °F; 90.5 K)
Boiling point	−161.3[3] °C (−258.3 °F; 111.8 K)
Hazards
GHS labelling:
Pictograms	[2]
Signal word	Danger[2]
Hazard statements	H220, H280[2]
Precautionary statements	P203, P210, P222, P280, P377, P381, P403, P410+P403[2]
Flash point	−188[3] °C (−306.4 °F; 85.1 K)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Monodeuterated methane (CH₃D) is an isotopologue of methane (CH₄).

It is a colorless, odorless gas. It is one of the partially deuterated isotopologues of methane. Due to the substitution of one hydrogen atom with deuterium, it exhibits measurable differences in physical and spectroscopic properties compared to fully protiated methane (methane) because of the mass effect and resulting changes in vibrational frequencies and moments of inertia.

it has a molar mass of 17.05 g/mol, intermediate between methane (16.04 g/mol) and perdeuterated methane (20.07 g/mol). Its physical constants are very close to those of methane, with small shifts due to isotopic substitution.

The vapor pressure of it is slightly lower than that of methane at the same temperature.

it belongs to the C_3v point group (lower symmetry than the T_d of methane). All nine vibrational modes are both infrared and Raman active, unlike methane where some modes are inactive in IR.

Notable shifts in vibrational frequencies include:

• C–H stretching modes: ~3000–3100 cm⁻¹
• C–D stretching mode: ~2200–2300 cm⁻¹ (significantly red-shifted compared to C–H)

These differences make it easily identifiable in infrared and Raman spectra and useful for spectroscopic studies of methane isotopologues. High-resolution ro-vibrational spectra of it have been extensively studied.

it possesses a small permanent dipole moment due to the isotopic asymmetry, allowing weak microwave rotational transitions (unlike methane and CD₄ which have zero dipole moment).

Chemically, it behaves similarly to methane but shows primary and secondary kinetic isotope effects in reactions involving C–H versus C–D bond cleavage. The C–D bond typically reacts more slowly, which is exploited in mechanistic studies and kinetic isotope effect (KIE) measurements.

it is widely used as an isotopic tracer in atmospheric chemistry, geochemistry, and reaction mechanism research. Its natural abundance in methane is used in clumped isotope studies to understand formation temperatures and origins of methane.

• Solubility in water and organic solvents is similar to methane.
• It is flammable and forms explosive mixtures with air, like methane.

• Methane