Solid phase
Official name
beta-Acetonitrile
Secondary names
Acetonitrile-HTM; beta-CH3CN; CH3CN-I
CAS number
75-05-8
Type
Family
molecular solid
Class
polar molecular solid
Compound type
nitrile
Chemical composition
Formula
$\beta-CH_3CN$
Chemical formula
CH3CN
Elemental formula
C2 H3 N
Isotope mixture type
terrestrial abundance
2.0
  Formula Name Family Number min-max Mole fraction Isotope mole fraction State Relevance
$CH_3CN$ Acetonitrile molecule 1 1.0 1 pure main
Chemical functions
  Function Number
$R-CH_3$ 1
$R-C \equiv N$ 1
Chemical bonds
  Bond Number
$\geq N \dots H-$ 2
$\geq C-H$ 3
$\equiv C-C\leq$ 1
$-C\equiv N$ 1
Class
molecular solids with polar molecules (02)
Type
with polyatomic organic polar molecules (CnHm...) (02.01)
Group
hydrocarbon with pnictogens (02.01.04)
Polymorphs
Phase name
beta-acetonitrile (phase I)
Phase type
crystalline
Crystal system
orthorhombic
Crystal class
pyramidal
Crystal class symbol
mm2 (C2v)
Crystal spacegroup
Cmc2(1)
Molar mass
41.053 $g/mol$
Density
1.058 $g/cm^3$
State NTP
liquid
Phase transitions
Phase transition type Other phases Temperature - Pressure
solid-gas from gas forms metastable beta phase by condensation below ~175K (~ -100°C) and stable beta phase by condensation above 216.9 K (-56.2°C)
solid-liquid from/to liquid 227-229 K (-46 - -44°C)
solid-solid to alpha-CH3CN below 216.9 K (-56.2°C) with slow cooling
solid-solid to alpha-CH3CN metastable beta phase transforms to alpha above ~205K
solid-solid from amorphous CH3CN above ~100-110 K (-173°C)
Phase transitions comments
beta-CH3CN is the high temperature phase but is the one formed upon crystallization of amorphous ice (kinetically metastable phase). It forms by condensation at temperature below about 175K and transforms to alpha phase at temperature around 205K but remains in beta phase when rapidly cooled to lower temperatures (supercooled phase)
Refringence type
biaxial
Refraction index $n_{\alpha}$
1.459 @ 140K
Pure color
colorless
Color
colorless
Diaphaneity
translucent
Luster
vitreous
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