[2.2]Paracyclophane
[CAS# 1633-22-3]

Identification

• Classification: Chemical reagent >> Organic reagent >> Aromatic hydrocarbon reagent
• Name: [2.2]Paracyclophane
• Synonyms: Di-p-xylylene; Tricyclo[8.2.2.24,7]hexadeca-4,6,10,12,13,15-hexaene
• Molecular Formula: C₁₆H₁₆
• Molecular Weight: 208.30
• CAS Registry Number: 1633-22-3
• EC Number: 216-644-2
• SMILES: C1CC2=CC=C(CCC3=CC=C1C=C3)C=C2

Properties

• Density: 1.0±0.1 g/cm³ Calc.^*
• Melting point: 285 - 288 °C (Expl.)
• Boiling point: 320.7±27.0 °C 760 mmHg (Calc.)^*
• Flash point: 154.0±14.4 °C (Calc.)^*
• Solubility: water: insoluble (Expl.)
• Index of refraction: 1.586 (Calc.)^*

^* Calculated using Advanced Chemistry Development (ACD/Labs) Software.

Safety Data

• Hazard Symbols: GHS07;GHS08 Warning
• Risk Statements: H317-H373
• Safety Statements: P260-P261-P272-P280-P302+P352-P319-P321-P333+P317-P362+P364-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Specific target organ toxicity - repeated exposure	STOT RE	2	H373
Skin sensitization	Skin Sens.	1B	H317
Skin sensitization	Skin Sens.	1	H317

Discovery and Applications

[2.2]Paracyclophane is a fascinating chemical compound that belongs to the family of cyclophanes, which are characterized by their unique three-dimensional structures with aromatic rings connected by bridges. The compound, with the molecular formula C16H16, features two benzene rings stacked in close proximity and held together by two ethylene bridges at the para-positions. This structure creates significant ring strain and leads to interesting chemical properties. First synthesized in the mid-20th century, [2.2]Paracyclophane has since attracted attention due to its novel structure and wide-ranging applications in materials science, organic chemistry, and electronics.

The discovery of [2.2]Paracyclophane is attributed to the pioneering work of Gerard Wittig and co-workers in 1949. The synthesis involved a Diels-Alder reaction followed by ring closure and dehydrogenation. This process was notable for the high degree of ring strain in the final product, which made the molecule challenging to synthesize. Since then, advances in synthetic techniques have allowed for the more efficient production of [2.2]Paracyclophane and its derivatives, leading to its expanded use in a variety of fields.

One of the most prominent applications of [2.2]Paracyclophane is in the development of conjugated polymers and organic electronic materials. Its strained structure and conjugated double bonds provide a unique combination of flexibility and electronic properties. In particular, [2.2]Paracyclophane derivatives, such as poly-p-xylylene, have been widely used as insulating materials in microelectronics and as protective coatings for electronic devices. These materials exhibit excellent thermal stability, chemical resistance, and electrical insulation, making them ideal for use in high-performance electronic components.

In the field of organic chemistry, [2.2]Paracyclophane is often used as a precursor for the synthesis of various functionalized derivatives. The proximity of the benzene rings in the structure allows for unusual chemical reactivity, including the ability to undergo selective substitutions and additions at specific positions. This property has made [2.2]Paracyclophane a valuable tool in the development of new organic reactions and the synthesis of complex molecular architectures. It is also used as a chiral scaffold for asymmetric catalysis, where its rigid structure helps induce stereoselectivity in certain reactions.

In recent years, [2.2]Paracyclophane has found applications in the area of surface coatings and polymer films. Its unique structure allows for the formation of thin, uniform films with excellent barrier properties, which are used in a variety of industries, including packaging, electronics, and biomedical devices. These films are often applied through chemical vapor deposition (CVD), a technique that takes advantage of [2.2]Paracyclophane’s ability to undergo polymerization when heated, forming highly durable and chemically inert coatings.

The potential of [2.2]Paracyclophane in molecular electronics is another area of ongoing research. Its conjugated system, combined with the rigid yet strained architecture, makes it an interesting candidate for the development of molecular wires and other nanoscale electronic components. Researchers are exploring the use of [2.2]Paracyclophane-based materials in organic light-emitting diodes (OLEDs), organic photovoltaics, and field-effect transistors. The ability to fine-tune the electronic properties of [2.2]Paracyclophane by introducing various substituents opens up a wide range of possibilities for its use in next-generation electronic devices.

From a structural perspective, [2.2]Paracyclophane’s strained ring system also presents opportunities for exploring fundamental aspects of molecular strain and aromaticity. The molecule has been the subject of numerous theoretical studies aimed at understanding the effects of ring strain on electronic distribution, reactivity, and physical properties. This research has provided valuable insights into the behavior of strained aromatic systems and has helped advance the broader field of physical organic chemistry.

In conclusion, [2.2]Paracyclophane is a unique chemical compound that continues to play a significant role in various scientific and industrial applications. Its discovery marked an important milestone in organic chemistry, and its distinctive structure has enabled its use in materials science, electronics, and catalysis. As research into cyclophanes and related compounds continues, [2.2]Paracyclophane is expected to remain an important subject of study and a valuable material in cutting-edge technologies.

References

2024. Recent progress in circularly polarized multi-resonance thermally activated delayed fluorescence materials for organic light-emitting diodes. Science China Chemistry, 67(11), 3456-3473.
DOI: 10.1007/s11426-024-2355-0

2022. Synthesis of optically active through-space conjugated polymers consisting of planar chiral pseudo-meta-disubstituted [2.2]paracyclophane. Polymer Journal, 54(12), 1429-1435.
DOI: 10.1038/s41428-022-00703-2

2023. Copper(I) complexes with planar chirality realize efficient circularly polarized electroluminescence. Science China Chemistry, 66(9), 2613-2620.
DOI: 10.1007/s11426-023-1635-5