In
chemistry, a chemical trap is a
chemical compound
A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one ele ...
that is used to detect unstable compounds. The method relies on efficiency of bimolecular reactions with reagents to produce a more easily characterize trapped product. In some cases, the trapping agent is used in large excess.
Case studies
Cyclobutadiene
A famous example is the detection of
cyclobutadiene
Cyclobutadiene is an organic compound with the formula . It is very reactive owing to its tendency to dimerize. Although the parent compound has not been isolated, some substituted derivatives are robust and a single molecule of cyclobutadiene is ...
released upon oxidation of
cyclobutadieneiron tricarbonyl. When this degradation is conducted in the presence of an alkyne, the cyclobutadiene is trapped as a bicyclohexadiene. The requirement for this trapping experiment is that the oxidant (ceric ammonium nitrate) and the trapping agent be mutually compatible.
:
Diphosphorus
Diphosphorus is an old target of chemists since it is the heavy analogue of N
2. Its fleeting existence is inferred by the controlled degradation of certain niobium complexes in the presence of trapping agents. Again, a Diels-Alder strategy is employed in the trapping:
:
Silylene
Another classic but elusive family of targets are
silylene
Silylene is a chemical compound with the formula SiH2. It is the silicon analog of methylene, the simplest carbene. Silylene is a stable molecule as a gas but rapidly reacts in a bimolecular manner when condensed. Unlike carbenes, which can exis ...
s,
analogues of carbenes. It was proposed that dechlorination of
dimethyldichlorosilane generates dimethylsilylene:
:SiCl
2(CH
3)
2 + 2 K → Si(CH
3)
2 + 2 KCl
This inference is supported by conducting the dechlorination in the presence of
trimethylsilane, the trapped product being pentamethyldisilane:
:Si(CH
3)
2 + HSi(CH
3)
3 → (CH
3)
2Si(H)-Si(CH
3)
3
Not that the trapping agent does not react with dimethyldichlorosilane or potassium metal.
Related meanings
In some cases, chemical trap is used to detect or infer a compound when present at
concentration
In chemistry, concentration is the abundance of a constituent divided by the total volume of a mixture. Several types of mathematical description can be distinguished: '' mass concentration'', '' molar concentration'', '' number concentration'' ...
s below its
detection limit
The limit of detection (LOD or LoD) is the lowest signal, or the lowest corresponding quantity to be determined (or extracted) from the signal, that can be observed with a sufficient degree of confidence or statistical significance. However, the ...
or is present in a mixture, where other components interfere with its detection. The trapping agent, for example a dye, reacts with the chemical to be detected, giving a product that is more easily detected.
References
{{Reflist
Analytical chemistry