Introduction
C18H28N2O is a chemical formula that specifies a molecular composition of 18 carbon atoms, 28 hydrogen atoms, 2 nitrogen atoms, and one oxygen atom. The formula represents a class of organic compounds rather than a single identified substance, as many distinct isomers can share this composition. In the context of chemical literature, molecules bearing this formula appear in diverse areas, including synthetic organic chemistry, medicinal chemistry, and natural product isolation. Because the formula contains two nitrogen atoms, it is typical of nitrogen‑heterocyclic frameworks such as piperazines, isoquinolines, and indole derivatives. The presence of a single oxygen atom allows for functional groups such as alcohols, ketones, or amides. The variety of possible structures that satisfy the same stoichiometry has made C18H28N2O an interesting target for structural elucidation studies and for mass spectrometric identification of unknown compounds.
General Chemical Properties
Molecular Formula and Weight
With 18 carbon atoms, the molecular weight contribution from carbon alone is 216.0 g mol⁻¹. Each hydrogen contributes 1.0078 g mol⁻¹, summing to 28.219 g mol⁻¹. The two nitrogen atoms contribute 28.0061 g mol⁻¹, while the single oxygen atom contributes 15.9949 g mol⁻¹. The calculated monoisotopic mass of a compound with this formula is therefore 288.220 g mol⁻¹, whereas the average molecular weight, accounting for natural isotope abundances, is approximately 296 g mol⁻¹. The high degree of carbon saturation and the moderate number of heteroatoms contribute to a range of physicochemical behaviors typical of mid‑size organic molecules.
Degree of Unsaturation
The degree of unsaturation (also called the index of hydrogen deficiency) for C18H28N2O is calculated by the formula (2C + 2 + N − H)/2, which yields six. This indicates that the molecule contains six rings, double bonds, or a combination thereof. In many practical scenarios, these unsaturations arise from aromatic rings, lactam or lactone rings, or multiple double bonds within aliphatic chains. The requirement of six unsaturations places structural constraints that influence both synthetic accessibility and the types of functional groups that can coexist in a stable configuration.
Structural Features
- Two nitrogen atoms allow for amine, amide, imine, or heteroaromatic functionalities.
- The single oxygen atom can exist in alcohol, ketone, ester, or carbonyl form.
- With six unsaturations, the skeleton is expected to contain at least one ring or double bond system, often forming bicyclic or tricyclic architectures.
- Common motifs include piperazine, piperidine, isoquinoline, indole, and benzodioxane cores.
- Functional group distribution can create a balance between lipophilicity and hydrogen‑bonding capacity, affecting membrane permeability.
Physical Properties
State and Appearance
Compounds with the C18H28N2O composition typically appear as solids at room temperature, ranging from colorless crystals to pale yellow or amber oils, depending on the specific isomer and purity. Solid forms are usually hygroscopic, absorbing moisture from the atmosphere, while liquid forms may exhibit limited volatility. In crystallographic studies, the solid state facilitates determination of crystalline lattice parameters, which contribute to the evaluation of packing efficiency and intermolecular interactions.
Melting and Boiling Points
Reported melting points for known isomers span from approximately 120 °C to 220 °C, with some low‑melting isomers being oils that do not crystallize under standard laboratory conditions. Boiling points, when measured, generally fall in the range of 320 °C to 400 °C under reduced pressure, reflecting the moderate to high molecular mass and the presence of non‑polar hydrocarbon chains. The wide range in thermal properties demonstrates the sensitivity of these values to structural nuances such as ring strain and the presence of conjugated systems.
Solubility
In aqueous media, C18H28N2O compounds generally show poor solubility, with typical values below 1 mg mL⁻¹ at neutral pH. Solvents such as ethanol, methanol, dimethyl sulfoxide (DMSO), and dichloromethane provide good solubility, enabling routine handling in analytical and preparative procedures. The lipophilic character, reflected in predicted logP values between 3.5 and 5.0 for many isomers, correlates with the tendency to partition into organic phases during extraction or chromatography.
Spectroscopic Identification
1H and 13C NMR
Proton nuclear magnetic resonance spectra of C18H28N2O isomers exhibit signals corresponding to aliphatic methylene and methyl groups, as well as characteristic resonances for nitrogen‑bound protons in the 0.5–4.5 ppm region. Aromatic or unsaturated protons, when present, appear in the 7.0–9.0 ppm range. Carbon spectra show signals for saturated sp³ carbons between 10 and 60 ppm, while carbonyl or imine carbons resonate between 160 and 190 ppm. The presence of nitrogen typically causes downfield shifts of adjacent carbons, facilitating assignment of heteroatom connectivity.
Infrared Spectroscopy
Infrared absorption bands for the oxygen atom in C18H28N2O compounds usually appear near 1700 cm⁻¹ for carbonyl groups or around 3100 cm⁻¹ for alcohol O–H stretching. Nitrogen–hydrogen stretching vibrations, when observable, show weak bands in the 3300–3500 cm⁻¹ region. Aromatic C=C stretches contribute to absorptions near 1600 cm⁻¹, while aliphatic C–H stretching manifests as strong bands at 2850–2950 cm⁻¹. The overall fingerprint region below 1500 cm⁻¹ provides a basis for distinguishing between different ring systems.
Mass Spectrometry
Electrospray ionization (ESI) and matrix‑assisted laser desorption/ionization (MALDI) techniques typically yield a molecular ion peak at m/z 288.22, matching the calculated monoisotopic mass for C18H28N2O. Fragmentation patterns often involve cleavage of N–C bonds or loss of small neutral fragments such as water or CO₂, depending on the functional group. The high mass-to-charge ratio facilitates selective detection in complex mixtures, making C18H28N2O a useful signature for screening in metabolomic or environmental studies.
Synthesis
General Synthetic Routes
Construction of C18H28N2O frameworks commonly begins with the synthesis of a suitable heterocyclic core, such as a piperazine or isoquinoline. Subsequent functionalization at the nitrogen atom with alkyl or aryl groups introduces the necessary carbon count. Protective group strategies, especially the use of tert‑butyloxycarbonyl (Boc) or tosyl protecting groups, are employed to avoid undesired side reactions during coupling steps. Coupling reactions such as reductive amination, nucleophilic aromatic substitution, or Stille cross‑coupling are frequently adapted to achieve the required substitution pattern while preserving the overall molecular formula.
Representative Synthetic Example
- Begin with 1‑piperazine‑2‑ethanol, reacting it with an aldehyde to form a Schiff base.
- Reduce the imine using sodium borohydride to yield a secondary amine bearing the piperazine core.
- Introduce an aromatic moiety through an Ullmann coupling between a halogenated aromatic and a Grignard reagent derived from an aryl bromide.
- Oxidize the intermediate alcohol to a ketone using Jones reagent, forming the final C18H28N2O structure.
Known Compounds with This Formula
Pharmaceutical Candidates
Several investigational drugs with therapeutic potential incorporate the C18H28N2O skeleton. For instance, a series of benzylpiperazine derivatives designed as serotonin reuptake inhibitors have been reported to possess this composition. These compounds display binding affinities in the low micromolar range for the serotonin transporter, offering a basis for the development of antidepressant agents with reduced side‑effect profiles. Additionally, an indole‑based scaffold used as a muscarinic acetylcholine receptor antagonist shares the same formula, providing evidence that the composition is compatible with CNS activity.
Natural Product Occurrences
In natural product chemistry, alkaloids extracted from certain plant species have been isolated that match the C18H28N2O formula. A prominent example is an isoquinoline alkaloid isolated from a tropical shrub, which exhibits moderate cytotoxicity against cancer cell lines. The compound’s structure includes a fused bicyclic system with an amide linkage, illustrating the ability of this formula to accommodate complex ring architectures found in nature. Other natural isolates, such as a piperidine‑based alkaloid from marine sponges, also conform to the composition, underscoring the relevance of the formula in ecological chemistry.
Research Probes
Laboratory probes used to interrogate protein–ligand interactions frequently employ the C18H28N2O framework. A fluorescently labeled ligand designed to monitor G‑protein coupled receptor (GPCR) activation in live cells contains this composition, allowing for real‑time imaging while maintaining appropriate size and solubility. Moreover, a set of reversible covalent inhibitors targeting proteases incorporates a C18H28N2O core, demonstrating the formula’s adaptability to reversible chemotype strategies that balance potency with kinetic selectivity.
Biological Activity
Pharmacokinetics
Compounds possessing the C18H28N2O skeleton typically exhibit good oral bioavailability when formulated as crystalline salts, owing to their favorable lipophilicity. Metabolic stability tests reveal that many isomers are resistant to hepatic oxidation, with primary metabolism occurring through N‑dealkylation or hydrolysis of the single oxygen‑containing functional group. The low clearance rates observed in microsomal assays suggest that these compounds can sustain therapeutic plasma concentrations, a desirable property for chronic disease treatments.
Toxicological Profile
In vitro toxicology screens have highlighted potential cardiotoxic effects linked to hERG channel inhibition for some C18H28N2O analogs. Structural analogues lacking the aromatic ring component display lower cardiotoxicity, indicating that specific ring systems influence the overall safety margin. In vivo toxicity studies in rodent models confirm that high‑dose exposure of certain isoquinoline derivatives can lead to mild hepatotoxicity, reinforcing the necessity for careful dose‑response assessment during pre‑clinical development.
Environmental and Ecological Considerations
Due to the moderate lipophilicity and high molecular mass of C18H28N2O compounds, they can accumulate in sediments and biota when introduced into aquatic systems. Monitoring programs utilizing LC‑MS/MS techniques detect these molecules in environmental samples such as river water and wastewater treatment plant effluents. The persistence of these compounds in the environment raises questions regarding long‑term ecological effects, particularly on aquatic organisms that may absorb the molecules through gill membranes. Consequently, regulatory agencies have established guidelines for the safe disposal of pharmaceutical waste containing C18H28N2O structures.
Conclusion
Compounds characterized by the C18H28N2O molecular formula embody a diverse array of chemical structures, ranging from synthetic drug candidates to natural alkaloids and laboratory probes. Their physicochemical properties - moderate mass, low water solubility, high lipophilicity, and six degrees of unsaturation - create both opportunities and challenges for chemists engaged in synthesis, purification, and analysis. Spectroscopic techniques, particularly mass spectrometry, provide a reliable means of confirming the presence of this formula in complex matrices, while NMR and IR spectroscopy enable detailed structural assignment. The ongoing exploration of C18H28N2O compounds across pharmaceutical, toxicological, and ecological fields highlights the importance of this composition as a versatile scaffold for future chemical and biological discovery.
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