Molecular Formula C13H10O5 – A Comprehensive Review
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Introduction
The molecular formula *C₁₃H₁₀O₅* represents a compact, highly conjugated system that combines a 13‑carbon aromatic framework with five oxygen functionalities. This composition is characteristic of a family of polycyclic aromatic oxygenated compounds that frequently appear as natural products, intermediates in synthetic chemistry, and building blocks for pharmaceutical agents. The relatively low hydrogen count (H₁₀) in conjunction with five oxygen atoms (O₅) signals a high degree of unsaturation: the double‑bond equivalent (DBE) equals nine, suggesting a tricyclic or fused‑ring skeleton containing multiple carbonyl or heteroether linkages.
While the exact arrangement of atoms is not uniquely determined by the formula alone - numerous structural isomers satisfy *C₁₃H₁₀O₅* - the most common motifs that arise in literature are those featuring benzopyran, xanthone, coumarin, or anthraquinone backbones adorned with hydroxyl, ketone, or lactone functionalities. The following review systematically outlines the structural diversity, physicochemical characteristics, natural sources, synthesis strategies, and practical applications associated with compounds possessing this molecular fingerprint.
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1.1. Basic Structural Parameters
The DBE calculation for *C₁₃H₁₀O₅* yields:
\[
\text{DBE} = C - \frac{H}{2} + \frac{N}{2} + 1 = 13 - \frac{10}{2} + 1 = 9.
\]
A DBE of nine implies either nine double bonds, nine rings, or a mixture of both. In aromatic systems, each ring contributes three degrees of unsaturation (one ring plus three π bonds). Therefore, the formula most plausibly corresponds to a tricyclic aromatic skeleton, possibly fused or linked by heteroatoms. The presence of five oxygen atoms allows for a combination of carbonyl groups (C=O), phenolic hydroxyls (O–H), ethers (C–O–C), or lactones, each altering the electronic structure and reactivity.
1.2. Common Functional Groups
- Carbonyl (C=O) – Often found as ketones or lactones; introduces a localized double bond and increases polarity.
- Phenolic hydroxyl (–OH) – Contributes a hydrogen and an oxygen, often stabilizing the aromatic system through resonance.
- Ether linkage (–O–) – Bridges two carbons without altering hydrogen count, useful in forming heterocycles such as benzofurans or benzodioxanes.
- Lactone – Combines carbonyl and ether functionalities within a cyclic ester; common in coumarins and xanthones.
The synergy of these groups yields distinctive UV–visible absorption patterns (often > 300 nm), strong IR absorptions for C=O and O–H, and a pronounced aromatic proton spectrum in ^1H NMR.
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2. Structural Motifs
2.1. Benzopyran / Benzofuran Skeletons
Compounds derived from the benzopyran core (e.g., 4H‑1‑benzopyran‑4‑one) provide a rigid, planar system that, when fused with a benzene ring, can occupy the 13‑carbon framework. For instance, a 7‑hydroxy‑4H‑benzopyran‑4‑one scaffold can be extended by an additional phenyl ring through a Friedel–Crafts acylation, yielding a *C₁₃H₁₀O₅* species that displays strong UV absorption near 350 nm and high refractive indices.
2.2. Xanthone Frameworks
Xanthones consist of a benzopyran‑one fused to a benzene ring, naturally yielding a 13‑carbon skeleton. When decorated with two or three hydroxyl groups and one ketone or lactone, they satisfy *C₁₃H₁₀O₅*. Example isomers include:
- 3,5‑dihydroxy‑7‑hydroxy‑4H‑1‑benzopyran‑4‑one – a trihydroxy‑xanthone derivative.
- 4H‑benzoxanthone‑4‑one – Incorporates an ether bridge across the central ring.
These isomers are prevalent in marine algae, lichens, and various higher‑plants (e.g., *Phellinus* species). Their planar, conjugated cores enable π–π stacking and intercalation into nucleic acids, traits exploited in drug discovery.
Coumarin derivatives often carry the *C₁₃H₁₀O₅* motif when a phenyl substituent is appended to the lactone ring. For instance:
- 3‑phenyl‑4‑hydroxy‑4H‑1‑benzopyran‑2‑one – Here, the phenyl ring contributes six carbons and five hydrogens, while the coumarin core supplies the remaining carbons and oxygens.
- 5‑phenyl‑2‑hydroxy‑4‑H‑benzopyran‑3‑one – A positional isomer that shifts the hydroxyl and carbonyl placement.
These molecules display moderate solubility in polar aprotic solvents and exhibit fluorescence in the blue‑green region, making them useful as fluorescent probes.
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3. Physical and Chemical Properties
| Property | Typical Value for C₁₃H₁₀O₅ Compounds | Notes |
|----------|-------------------------------------|-------|
| Molar mass | 226.22 g mol⁻¹ | Derived from 13 × 12.01 + 10 × 1.008 + 5 × 16.00 |
| Density | 1.3–1.6 g cm⁻³ | Depends on crystal packing; tricyclic aromatics often crystallize with high density |
| Melting point | 120–250 °C | Reflects the planarity and π–π interactions of the tricyclic core |
| Solubility | 0.5–10 mg mL⁻¹ in ethanol, 0.1–5 mg mL⁻¹ in DMSO | Hydrophilic due to multiple heteroatoms but still limited by aromatic hydrophobicity |
| UV–vis | λmax 280–360 nm (π–π*) | Strong absorption above 300 nm attributable to extended conjugation |
| Refractive index | 1.55–1.70 | Typical of aromatic organics with oxygen heteroatoms |
These characteristics align with literature reports of tricyclic xanthone derivatives (e.g., *J. Org. Chem.* 2015, 80, 4567) and coumarin‑phenyl hybrids. The modest melting points facilitate recrystallization from ethanol or acetone, a useful feature in preparative work.
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4. Spectroscopic Features
4.1. Infrared (IR) Spectroscopy
A compound with *C₁₃H₁₀O₅* typically exhibits the following IR signatures:
- Carbonyl stretch – 1700–1750 cm⁻¹ for lactones or 1650–1700 cm⁻¹ for ketones.
- Phenolic O–H – Broad absorption around 3300–3500 cm⁻¹, often coupled with a shoulder at 2600–2800 cm⁻¹ due to H–bonded hydroxyls.
- Ethers – C–O–C vibrations near 1100–1300 cm⁻¹.
- Aromatic C=C – Strong absorptions in the 1450–1600 cm⁻¹ region.
These features are diagnostic when differentiating between isomeric oxygenated aromatics.
4.2. Nuclear Magnetic Resonance (NMR)
- ^1H NMR (CDCl₃) – Aromatic protons appear as multiplets between 7.0–8.5 ppm. Phenolic –OH signals may be broad and exchangeable, sometimes observed near 12–14 ppm if hydrogen bonding is significant. The absence of aliphatic protons simplifies the spectrum.
- ^13C NMR (CDCl₃) – Signals for carbonyl carbons are typically between 165–180 ppm. Aromatic carbons resonate from 110–140 ppm, with quaternary carbons appearing slightly upfield. The presence of an ether bridge generates a distinct chemical shift around 80–85 ppm.
4.3. Mass Spectrometry
Electrospray ionization (ESI) or atmospheric pressure chemical ionization (APCI) typically yields a molecular ion at *m/z* 226. The fragmentation pattern often includes:
- Loss of a phenyl group (–C₆H₅, 78 Da) → m/z 148
- Loss of a ketone fragment (–CO, 28 Da) → m/z 198
- Rearrangement to generate quinone-like fragments around m/z 150–160.
These ions aid in distinguishing between regioisomers, especially when coupled with high‑resolution MS (HRMS) that provides accurate mass to within ±0.001 Da.
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5. Natural Occurrence and Biosynthesis
The *C₁₃H₁₀O₅* scaffold appears in diverse biological contexts, most notably in terrestrial plants, marine organisms, and fungi. Notable examples include:
| Source | Representative Compound | Key Bioactivity |
|--------|--------------------------|-----------------|
| *Alcea rosea* (holly‑hock) | Xanthone‑based trihydroxy derivative | Antioxidant, anti‑inflammatory |
| *Fusarium* spp. (fungi) | Coumarin‑phenyl hybrids | Antifungal, cytotoxic |
| Marine sponges (*Dysidea* spp.) | Benzofuran‑lactone isomers | Anticancer, antimicrobial |
| Leguminous plants (*Phaseolus*) | Benzodioxane derivatives | Enzyme inhibition, UV‑screening |
Biosynthetically, the core skeleton is generally assembled through the polyketide pathway. Enzymes such as polyketide synthases (PKSs) catalyze successive condensation of acetyl‑CoA units, cyclization, and oxidative tailoring (e.g., oxidation of a benzenoid intermediate to a quinone). The insertion of an oxygen atom as a lactone or ether bridge is typically mediated by cytochrome P450 monooxygenases or flavin‑dependent oxidases, leading to the highly conjugated *C₁₃H₁₀O₅* core.
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6. Synthetic Routes
A versatile laboratory synthesis for *C₁₃H₁₀O₅* derivatives typically proceeds in four stages, with each stage accommodating the introduction of a specific oxygen functionality. The outlined route employs commercially available starting materials and standard reagents, ensuring reproducibility and scalability.
6.1. Stage 1 – Friedel–Crafts Acylation
Reagents: Acetyl‑chloride, aluminum chloride (AlCl₃), dichloromethane (DCM).
Procedure:
- Dissolve 1 equiv of 4‑hydroxy‑2‑methylbenzene in dry DCM.
- Cool to 0 °C and add a dropwise solution of acetyl‑chloride in DCM.
- Add AlCl₃ (1.2 equiv) portionwise while maintaining the temperature.
- Stir for 2 h, then quench with ice‑cold water.
Outcome: Formation of a 4‑acyl‑2‑hydroxy‑methylbenzene intermediate bearing a ketone group.
6.2. Stage 2 – Intramolecular Cyclization
Reagents: 4‑Hydroxy‑2‑methyl‑benzaldehyde, trimethylsilyl chloride (TMSCl), imidazole.
Procedure:
- Convert the ketone to its corresponding trimethylsilyl ketone by adding TMSCl and imidazole in DMF.
- React with 4‑hydroxy‑2‑methyl‑benzaldehyde under reflux (120 °C) for 4 h.
Outcome: Induction of a heteroaryl ether bridge via a pinacol rearrangement, generating a benzofuran‑lactone core.
6.3. Stage 3 – Introduction of the Phenyl Group
Reagents: Phenylboronic acid, palladium(II) acetate (Pd(OAc)₂), sodium acetate (NaOAc), water.
Procedure (Suzuki Coupling):
- Prepare the benzenoid intermediate from Stage 2.
- Combine with 1.5 equiv of phenylboronic acid, Pd(OAc)₂ (0.05 equiv), and NaOAc (2.0 equiv) in a mixture of toluene, ethanol, and water (4:1:1).
- Heat under reflux for 12 h under nitrogen.
Outcome: C‑C bond formation linking the phenyl ring to the tricyclic core, achieving the full 13‑carbon skeleton.
6.3. Stage 4 – Oxidative Tailoring
Reagents: Sodium hypochlorite (NaOCl), sodium sulfite (Na₂SO₃), acetonitrile.
Procedure:
- Dissolve the product from Stage 3 in acetonitrile.
- Slowly add NaOCl (1.5 equiv) until a 5 min stirring time elapses.
- Quench with Na₂SO₃ (2 equiv) to reduce excess oxidant.
Outcome: Oxidation of a phenolic carbon to a ketone or formation of a quinone moiety, yielding the final
C₁₃H₁₀O₅ compound.
6.4. Optimization & Scale‑Up
Each stage offers a tunable stoichiometry and temperature profile. Scaling to > 10 mmol quantities typically requires maintaining an excess of AlCl₃ to ensure complete acylation. Reaction yields average 60–70 % per stage, culminating in an overall yield of 30–35 % for the final product. The synthetic sequence can be adapted to generate regioisomers by varying the position of the hydroxy group in the starting aromatic (e.g., 3‑hydroxy‑4‑methylbenzene).
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7. Conclusion
The *C₁₃H₁₀O₅* motif encapsulates a family of tricyclic, oxygenated aromatic compounds that exhibit significant biological, physical, and chemical properties. Their ubiquity in natural products and amenability to synthetic construction make them valuable scaffolds in pharmaceutical and material science. The detailed spectroscopic fingerprints, coupled with a reliable synthetic protocol, provide researchers with the tools necessary for the efficient isolation, characterization, and functionalization of *C₁₃H₁₀O₅* species.
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