Introduction
C18H20N2 denotes a molecular composition consisting of eighteen carbon atoms, twenty hydrogen atoms, and two nitrogen atoms. The empirical formula is C9H10N1, indicating that the molecule contains nine carbon atoms, ten hydrogen atoms, and one nitrogen atom in its simplest ratio. The presence of two nitrogen atoms suggests the existence of heterocyclic or amine functionalities, while the relatively high carbon count indicates a substantial aromatic or aliphatic framework. Compounds sharing this molecular formula encompass a variety of structural motifs, including bicyclic aromatic systems, fused heterocycles, and alkylated amines. The diversity of possible arrangements provides a wide range of physicochemical properties and biological activities, which is why molecules with the C18H20N2 composition are frequently encountered in medicinal chemistry, material science, and natural product research.
Chemical Identity
Molecular Formula and Composition
The formula C18H20N2 is specified by the atomic counts: 18 carbons, 20 hydrogens, and 2 nitrogens. This composition yields a molecular weight of 264.36 g·mol⁻¹ when atomic masses are taken as 12.01 g·mol⁻¹ for carbon, 1.008 g·mol⁻¹ for hydrogen, and 14.01 g·mol⁻¹ for nitrogen. The molecule may be neutral or carry a positive or negative charge depending on the presence of protonated or deprotonated amine groups; however, the most common neutral form corresponds to a fully hydrogenated structure.
Molecular Weight
The calculated molecular weight of 264.36 g·mol⁻¹ places the compound within the range of small organic molecules. This weight is consistent with a moderate number of rotatable bonds and suggests a balance between lipophilicity and aqueous solubility. The mass is also within the detection limits of typical mass spectrometric techniques, allowing facile confirmation of the formula via electron ionization or electrospray ionization methods.
Empirical Formula and Degree of Unsaturation
Using the empirical formula C9H10N1, the degree of unsaturation (double bond equivalents, DBE) can be calculated by the formula DBE = C − H/2 + N/2 + 1. Substituting the empirical counts gives DBE = 9 − 10/2 + 1/2 + 1 = 9 − 5 + 0.5 + 1 = 5.5. Since a fractional DBE is not physically meaningful, the empirical formula may be simplified further to C9H12N1 (which yields DBE = 6). This indicates that the molecule contains six rings or double bonds, consistent with aromatic or fused-ring systems commonly observed in heterocyclic compounds of this formula class.
Structural Features
Possible Structural Isomers
Numerous structural isomers can be constructed with the C18H20N2 formula. These include linear alkylamines with aromatic substituents, bicyclic systems such as indole or phenanthridine derivatives, and fused heterocycles incorporating pyridine, pyrimidine, or quinoline rings. The position of the nitrogen atoms dramatically influences the electronic properties of the molecule, as does the presence of alkyl or aryl side chains. In many cases, isomerism arises from the location of a secondary amine (e.g., anilino versus secondary alkyl amine), the presence of a fused benzene ring, or the substitution pattern on an aromatic core.
Common Functional Groups
Compounds with this composition frequently feature the following functional groups:
- Secondary amines or amide linkages, providing basic or nucleophilic sites.
- Aromatic rings, including mono- or fused benzene rings, which contribute to conjugation.
- Heteroaromatic systems such as pyridine or indole, where nitrogen atoms participate in aromatic sextets.
- Alkyl chains attached to nitrogen or aromatic carbons, influencing lipophilicity and steric bulk.
The interplay between these groups determines the overall polarity, reactivity, and potential for intermolecular interactions such as hydrogen bonding or π–π stacking.
Three‑Dimensional Conformation
Three‑dimensional conformations vary considerably among isomers. Aromatic cores typically adopt planar geometries, while alkyl substituents introduce flexibility. Secondary amine nitrogen atoms can act as rotatable bonds, creating conformational isomers that may interconvert at ambient temperatures. In fused heterocycles, such as quinoline analogues, steric hindrance between adjacent rings can lead to non‑planar arrangements, influencing the overall dipole moment and packing behavior in the solid state.
Physical Properties
State at Room Temperature
Depending on the specific isomer, C18H20N2 compounds are usually solid crystals or oils at room temperature. Aromatic heterocycles with extended conjugation tend to crystallize as rigid, colorless or pale yellow solids, whereas highly aliphatic derivatives may remain liquid due to reduced intermolecular interactions.
Melting and Boiling Points
Melting points for this class of compounds typically range between 150 °C and 250 °C. The variation is largely attributable to the degree of aromaticity and the presence of rigid, fused ring systems. Boiling points, measured under reduced pressure to avoid decomposition, generally fall between 300 °C and 400 °C. These high boiling points reflect strong van der Waals forces and potential hydrogen bonding among molecules containing amine or amide functionalities.
Solubility
Solubility is highly dependent on the substitution pattern. Aromatic derivatives with polar amine groups exhibit good solubility in polar organic solvents such as ethanol, methanol, and dimethyl sulfoxide. Conversely, highly lipophilic isomers with long alkyl chains display limited solubility in water but dissolve readily in nonpolar solvents such as hexane or dichloromethane. The solubility of solid isomers in water is typically below 1 mg mL⁻¹, indicating low aqueous compatibility unless protonated to form salts.
Optical Properties
Many C18H20N2 compounds exhibit characteristic UV–Vis absorption bands arising from π–π* transitions in aromatic systems. Wavelengths commonly fall in the range of 220 nm to 280 nm, with molar absorptivities ranging from 5 000 to 20 000 M⁻¹ cm⁻¹. In some cases, extended conjugation leads to bathochromic shifts, enabling absorption in the visible region, which can be exploited for dye or chromophore applications.
Synthesis
General Synthetic Strategies
Synthesis of molecules with the C18H20N2 formula generally follows one of the following strategies:
- Condensation reactions between aryl halides and amines or ammonia.
- Reductive amination of ketones or aldehydes with primary or secondary amines.
- Friedel–Crafts alkylation or acylation of heteroaromatic substrates.
- Cyclization reactions such as intramolecular nucleophilic aromatic substitution (SNAr) or intramolecular amidation.
Choice of strategy is guided by the desired substitution pattern and the availability of starting materials.
Specific Synthetic Routes
One common route involves the Suzuki–Miyaura cross‑coupling of a 3‑bromopyridine with a phenylboronic acid to afford a biaryl scaffold, followed by reductive amination of an aldehyde group on the pyridine ring with a secondary amine to introduce the second nitrogen atom. Alternatively, a nucleophilic aromatic substitution between a 4‑fluoropyridine and aniline derivatives can generate a substituted pyridinyl aniline, which may then undergo intramolecular cyclization to form fused heterocyclic systems such as phenanthridine.
Friedel–Crafts Alkylation
In the Friedel–Crafts alkylation approach, an aryl bromide is reacted with an alkylating agent (e.g., benzyl bromide) in the presence of a Lewis acid catalyst such as AlCl₃. The resulting alkylated arene is then functionalized with a nitrogen‑bearing side chain via nucleophilic attack by an amine or an amide coupling reagent, such as HATU or DCC, which activates the carboxylic acid to form an amide linkage. Subsequent deprotection or rearrangement steps yield the target compound.
Cyclization Reactions
Cyclization often serves to form fused ring systems. For instance, treating a 2‑(bromomethyl)pyridine with a secondary amine in a basic medium can lead to intramolecular amidation, producing a quinoline‑derived lactam. Similarly, an intramolecular SNAr between a chlorinated heteroaromatic core and a pendant amine can produce phenanthridine derivatives. These cyclizations typically proceed at elevated temperatures (120 °C–160 °C) and benefit from the electron‑withdrawing nature of the heteroaromatic ring, which activates the electrophilic carbon toward nucleophilic attack.
Reaction Conditions and Optimization
Optimizing reaction conditions involves controlling temperature, solvent polarity, and catalyst loading. Suzuki couplings typically require a palladium catalyst (e.g., Pd(PPh₃)₄) and a base such as K₂CO₃, conducted in a mixture of water and organic solvent (e.g., toluene). Reductive amination is usually carried out with NaBH₃CN in a solvent such as methanol or ethanol, with the reaction mixture acidified to promote imine formation. Friedel–Crafts reactions benefit from the use of strong Lewis acids and require careful monitoring to avoid poly‑alkylation or over‑acylation.
Biological Activity and Applications
Medicinal Chemistry
Compounds bearing the C18H20N2 composition are frequently evaluated for antiproliferative, antidiabetic, or CNS‑acting properties. The presence of two nitrogen atoms allows for interaction with a range of biological targets, including enzymes such as tyrosine kinases, proteases, and monoamine oxidases. Structural features such as a pyridinyl aniline core or an indole moiety often confer high binding affinity to protein targets, while alkylation of nitrogen atoms can modulate pharmacokinetic attributes such as metabolic stability and membrane permeability.
Material Science
Due to their conjugated systems, several C18H20N2 molecules are incorporated into organic electronic materials. For instance, nitrogen‑containing polyaromatic systems are used as building blocks for organic light‑emitting diodes (OLEDs) or as electron‑transport layers in solar cells. The ability to fine‑tune electronic properties through substitution patterns makes these molecules attractive for the design of push–pull chromophores, which exhibit desirable photophysical behavior in solid or solution phases.
Natural Product Research
Some natural alkaloids, especially those derived from marine organisms or plants, share the C18H20N2 formula. These alkaloids often possess a fused heterocyclic core and contain secondary amine functionalities that contribute to their bioactivity, such as antimicrobial or cytotoxic effects. Extraction and isolation of these natural products typically involve chromatographic techniques (flash chromatography, preparative HPLC) followed by spectral analysis to confirm the formula.
Occurrence
Natural Occurrence
Examples of naturally occurring C18H20N2 molecules include certain indole alkaloids isolated from marine sponges and terrestrial plants. These alkaloids frequently display complex substitution patterns that arise from enzymatic processes during biosynthesis, such as methylation, hydroxylation, or prenylation. The natural products often exhibit potent bioactivity, which is leveraged in pharmacological studies to identify lead compounds for drug development.
Anthropogenic Production
Anthropogenic routes to C18H20N2 molecules are dominated by synthetic organic chemistry processes. Industrial laboratories produce these compounds at scale for use as intermediates in pharmaceuticals, agrochemicals, or specialty polymers. Large‑scale production often employs robust cross‑coupling reactions or reductive amination steps that allow efficient conversion of inexpensive starting materials into the desired heterocyclic structures.
Safety and Handling
Hazard Identification
Compounds with the C18H20N2 formula can present hazards associated with their amine functionalities. These hazards include:
- Flammability: oils or solids may be flammable, especially if they contain long alkyl chains.
- Corrosiveness: basic amines can corrode metals and cause skin irritation.
- Carcinogenicity: some aromatic heterocycles have been classified as potential carcinogens based on in vitro and in vivo studies.
- Reproductive toxicity: certain amine‑bearing derivatives have been identified as teratogenic in animal models.
Precise hazard classification requires evaluation of the specific isomer and its exposure route.
Risk Assessment
Risk assessment should consider the concentration, duration of exposure, and route of entry. Inhalation of dust from powdered solid isomers poses a risk of respiratory irritation. Dermal contact with oils containing free amine groups can lead to irritation or absorption through the skin. Ingestion of these compounds is strongly discouraged, as oral exposure may result in systemic toxicity.
Regulatory Status
Regulatory classification varies by jurisdiction. In the United States, many of these molecules are listed as chemicals of concern under the Toxic Substances Control Act (TSCA). In the European Union, certain analogues are subject to the European Chemicals Agency (ECHA) classification system and may require registration under REACH. Compliance with these regulations mandates appropriate labeling and reporting of potential hazards.
Safe Working Practices
When handling C18H20N2 compounds, researchers should employ the following practices:
- Use of appropriate personal protective equipment, including gloves, lab coats, and eye protection.
- Conducting work in a well‑ventilated fume hood to avoid inhalation of vapors or dust.
- Storage of solids in tightly sealed containers at reduced temperatures to minimize degradation.
- Implementation of spill containment protocols, with immediate neutralization of spills using dilute acid or base depending on the amine protonation state.
Related Compounds
Isomeric Forms
Isomeric diversity among C18H20N2 molecules is vast. Structural isomers can be differentiated by the position of the nitrogen atoms (e.g., pyridine‑aniline versus indole‑alkylamine), the degree of ring fusion (e.g., phenanthridine versus quinoline), or the presence of side chains (e.g., tert‑butyl versus methyl groups). Such isomers may exhibit markedly different spectral signatures and biological profiles.
Analogues with Similar Formula
Other molecules share the same elemental counts but differ in molecular shape. Examples include C18H20N3 derivatives with an additional nitrogen atom, which introduce amide or imidazole functionalities. Likewise, C18H20O2 analogues contain two oxygen atoms instead of nitrogen, producing different reactivity patterns. Comparative analysis of these analogues aids in the systematic exploration of structure–activity relationships within this chemical space.
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