Chemical compound
Methylidyne
, or (
unsubstituted
)
carbyne
, is an
organic compound
whose molecule consists of a single
hydrogen
atom
bonded
to a
carbon
atom. It is the parent compound of the
carbynes
, which can be seen as obtained from it by substitution of other
functional groups
for the hydrogen.
The carbon atom is left with either one or three unpaired
electrons
(unsatisfied
valence
bonds), depending on the molecule's
excitation state
; making it a
radical
. Accordingly, the
chemical formula
can be CH
?
or CH
3?
(also written as
?
CH); each dot representing an unpaired electron. The corresponding systematic names are
methylylidene
or
hydridocarbon(?)
, and
methanetriyl
or
hydridocarbon(3?)
. However, the formula is often written simply as CH.
Methylidyne is a highly
reactive
gas, that is quickly destroyed in ordinary conditions but is abundant in the
interstellar medium
(and was one of the first
molecules
to be detected there).
[4]
Nomenclature
[
edit
]
The
trivial name
carbyne
is the
preferred IUPAC name
.
Following the substitutive nomenclature, the molecule is viewed as methane with three hydrogen atoms removed, yielding the systematic name "methylidyne".
Following the additive nomenclature, the molecule is viewed as a hydrogen atom bonded to a carbon atom, yielding the name "hydridocarbon".
By default, these names pay no regard to the excitation state of the molecule. When that attribute is considered, the states with one unpaired electron are named "methylylidene" or "hydridocarbon(?)", whereas the excited states with three unpaired electrons are named "methanetriyl" or "hydridocarbon(3?)".
Bonding
[
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]
As an odd-electron species, CH is a radical. The ground state is a doublet (
X
2
Π). The first two excited states are a quartet (with three unpaired electrons) (
a
4
Σ
?
) and a doublet (
A
2
Δ). The quartet lies at 71 kJ/mol above the ground state.
[5]
Reactions of the doublet radical with non-radical species involves insertion or addition:
- [CH]
?
(
X
2
Π) +
H
2
O
→ H
?
+ C
H
2
O (major) or
[CH
2
(OH)]
?
whereas reactions of the quartet radical generally involves only abstraction:
- [CH]
3?
(
a
4
Σ
?
) +
H
2
O
→
[CH
2
]
+ [HO]
?
Methylidyne can bind to metal atoms as
tridentate ligand
in
coordination complexes
. An example is
methylidynetricobaltnonacarbonyl
HCCo
3
(CO)
9
.
[6]
Occurrence and reactivity
[
edit
]
Fischer?Tropsch intermediate
[
edit
]
Methylidyne-like species are implied intermediates in the
Fischer?Tropsch process
, the
hydrogenation
of CO to produce
hydrocarbons
. Methylidyne entities are assumed to bond to the
catalyst
's surface. A hypothetical sequence is:
[6]
- M
n
CO +
1
/
2
H
2
→ M
n
COH
- M
n
COH + H
2
→ M
n
CH + H
2
O
- M
n
CH +
1
/
2
H
2
→ M
n
CH
2
The M
n
CH intermediate has a tridentate methylidine ligand. The
methylene ligand
(H
2
C) is then poised couple to CO or to another methylene, thereby growing the C?C chain.
[7]
Amphotericity
[
edit
]
The methylylidyne group can exhibit both
Lewis acidic and Lewis basic
character.
[8]
Such behavior is only of theoretical interest since it is not possible to produce methylidyne.
In interstellar space
[
edit
]
In October 2016, astronomers reported that the methylidyne radical
?
CH, the carbon-hydrogen positive ion
:
CH
+
, and the carbon ion
?
C
+
are the result of
ultraviolet light
from
stars
, rather than in other ways, such as the result of turbulent events related to
supernovas
and
young stars
, as thought earlier.
[9]
Preparation
[
edit
]
Methylidyne can be prepared from
bromoform
.
[6]
See also
[
edit
]
References
[
edit
]
- ^
Henri A. Favre; Warren H. Powell (2014).
Nomenclature of Organic Chemistry : IUPAC Recommendations and Preferred Names 2013
. Cambridge, England: Royal Society of Chemistry. p. 1054.
ISBN
978-0-85404-182-4
.
- ^
"hydridocarbon (CHEBI:51382)"
.
Chemical Entities of Biological Interest (ChEBI)
. UK: European Bioinformatics Institute. IUPAC Name.
- ^
"
hydridocarbon(3?)
". Substance page at the Chemical Entities of Biological Interest (ChEBI) website, European Bioinformatics Institute, UK. Accessed on 2019-04-20
- ^
Encyclopedia of Astrobiology, Volume 1 edited by Ricardo Amils, Jose Cernicharo Quintanilla, Henderson James Cleaves, William M. Irvine, Daniele Pinti, Michel Viso. 2011, Springer: Heidelberg
- ^
Brooks, Bernard R.; Schaefer III, Henry F. (1 December 1977). "Reactions of Carbynes. Potential Energy Surfaces for the Doublet and Quartet Methylidyne (CH) Reactions with Molecular Hydrogen".
The Journal of Chemical Physics
.
67
(11): 5146?5151.
Bibcode
:
1977JChPh..67.5146B
.
doi
:
10.1063/1.434743
.
- ^
a
b
c
Nestle, Mara O.; Hallgren, John E.; Seyferth, Dietmar; Dawson, Peter; Robinson, Brian H. (1 January 1980).
"μ
3
-Methylidyne and μ
3
-Benzylidyne-Tris(Tricarbonylcobalt)"
. In Busch, Daryle H. (ed.).
Inorganic Syntheses, Vol. 20
. John Wiley & Sons, Inc. pp.
226?229
.
doi
:
10.1002/9780470132517.ch53
.
ISBN
9780470132517
.
- ^
W. A. Herrmann "Organometallic Aspects of the Fischer-Tropsch Synthesis" Angewandte Chemie International Edition in English, 1982, Volume 21, Issue 2, pages 117?130.
doi
:
10.1002/anie.198201171
- ^
Anderson, Stuart M.; McCurdy, K. E.; Kolb, C. E. (February 1989). "The Methylidyne Radical + Carbon Monoxide Reaction: Rate Coefficient for Carbon Atom Exchange at 294 K".
The Journal of Physical Chemistry
.
93
(3): 1042?1048.
doi
:
10.1021/j100340a007
.
- ^
Landau, Elizabeth (12 October 2016).
"Building Blocks of Life's Building Blocks Come From Starlight"
.
Jet Propulsion Laboratory
.
NASA
. Retrieved
13 October
2016
.