Introduction
C13H10O5 is a molecular formula that defines a class of organic compounds containing thirteen carbon atoms, ten hydrogen atoms, and five oxygen atoms. The formula represents a variety of structural motifs, many of which include aromatic rings and functional groups such as phenols, ketones, and carboxylic acids. Because the formula does not specify connectivity, it can correspond to multiple isomers, each with distinct chemical behavior and potential applications. The study of compounds with this formula is relevant to fields ranging from natural product chemistry to materials science and medicinal chemistry.
Structural Features and Degree of Unsaturation
The degree of unsaturation (also called the index of hydrogen deficiency) for a compound with the formula C13H10O5 is calculated as follows: 2C + 2 – H = 2(13) + 2 – 10 = 18. Dividing by two yields 9. Thus, the compound possesses nine rings and/or double bonds. In most practical cases, the unsaturation arises from three aromatic rings (each accounting for four degrees) and additional unsaturated functionalities such as ketones or carboxyl groups. This framework suggests that typical structures include tricyclic aromatic systems with attached oxygenated substituents.
Common Structural Motifs
- Benzophenone core: Benzophenone itself has the formula C13H10O and is a key scaffold for many derivatives. Adding oxygenated groups to the aromatic rings yields compounds with the C13H10O5 formula.
- Phenolic substitutions: Hydroxyl groups attached to benzene rings contribute one oxygen each without increasing the carbon count, thereby raising the total oxygen number while keeping the hydrogen count relatively unchanged.
- Ketone and aldehyde groups: Carbonyl functionalities add oxygen atoms and may influence the hydrogen count depending on the substitution pattern.
- Carboxylate esters: Esterification of carboxyl groups can modify the formula while preserving the overall carbon skeleton.
Representative Isomers
Although the formula is generic, several notable isomers have been isolated and characterized. The following examples illustrate the diversity of structures that satisfy the C13H10O5 composition.
1,3,5‑Trihydroxybenzophenone
This compound features a benzophenone core with hydroxyl groups at the 1, 3, and 5 positions of one aromatic ring. The presence of three phenolic groups increases the oxygen count to five while maintaining the hydrogen count at ten.
4‑Hydroxybenzophenone‑3 (Oxybenzone)
Oxybenzone is a widely used sunscreen agent with the formula C14H12O3. While it does not match C13H10O5 exactly, structural analogs such as 4‑hydroxybenzophenone‑3‑butyl ester demonstrate the flexibility of the benzophenone scaffold to accommodate additional oxygen atoms without altering the carbon framework drastically.
Anthraquinone‑2,7‑Diol
Anthraquinone‑2,7‑diol consists of an anthracene backbone with two keto groups and two hydroxyl groups. The resulting molecular formula is C14H10O4, which differs by one carbon and one oxygen but serves as a conceptual bridge to C13H10O5 isomers that may arise from ring cleavage or substitution.
Flavone Derivatives
Flavones such as 4′‑hydroxyflavone contain a 15‑carbon skeleton. Dehydrogenation or removal of two carbon atoms (e.g., by decarboxylation) can yield a 13‑carbon variant that retains the essential flavone core while adding additional hydroxyl groups to meet the oxygen count.
Physical and Chemical Properties
Compounds with the C13H10O5 formula generally exhibit low solubility in nonpolar solvents and moderate solubility in polar solvents such as ethanol or methanol due to the presence of multiple hydrogen‑bonding sites. Melting points tend to range from 120 °C to 220 °C, reflecting the balance between aromatic ring stability and the polar interactions introduced by hydroxyl and carbonyl groups.
Reactivity
- Electrophilic aromatic substitution: Phenolic groups activate adjacent rings toward substitution, allowing the introduction of halogens, nitration, or sulfonation under controlled conditions.
- Redox behavior: The presence of hydroxyl groups confers antioxidant activity, enabling electron donation to neutralize free radicals. Conversely, ketone groups can undergo nucleophilic addition or reduction to alcohols.
- Acid–base characteristics: Phenolic protons exhibit pK_a values between 9 and 11, rendering the compounds weak acids in aqueous solution.
Synthesis Methods
Industrial and laboratory synthesis of C13H10O5 compounds typically follows one of two strategies: (1) direct functionalization of a benzophenone core, or (2) assembly of the aromatic skeleton from simpler precursors via cross‑coupling reactions.
1. Functionalization of Benzophenone
- Methylation or hydroxylation: Starting from commercially available benzophenone, selective hydroxylation at desired positions can be achieved via directed ortho metalation followed by quenching with electrophilic oxygen sources.
- Oxidative coupling: Using metal catalysts (e.g., Pd or Cu) in the presence of oxidants such as persulfate, two phenyl rings can be coupled to form a benzophenone skeleton bearing additional oxygen functionalities.
- Ketone formation: Introduction of additional carbonyl groups is accomplished through Friedel–Crafts acylation or oxidation of methyl groups adjacent to the aromatic system.
2. Cross‑Coupling Approaches
- Suzuki–Miyaura coupling: Organoboron reagents bearing phenolic or alkyl substituents are coupled with aryl halides under palladium catalysis, yielding complex polyaromatic structures.
- Stille coupling: Organostannane reagents provide a versatile route to construct aromatic rings while incorporating functional groups that contribute to the oxygen count.
- Negishi coupling: Organozinc species can be employed when steric hindrance is a concern, allowing the synthesis of densely substituted tricyclic aromatics.
Spectroscopic Characterization
Accurate structural determination of C13H10O5 compounds relies on a combination of nuclear magnetic resonance (NMR), mass spectrometry (MS), infrared (IR) spectroscopy, and X‑ray crystallography. Each technique contributes complementary information that confirms the connectivity of atoms and the nature of functional groups.
Nuclear Magnetic Resonance
Proton NMR spectra typically display aromatic multiplets between 6.5 ppm and 8.5 ppm, with down‑field shifts for protons ortho to hydroxyl groups. Hydroxyl protons appear as broad singlets or doublets between 9.5 ppm and 12.5 ppm, depending on hydrogen‑bonding patterns. Carbon‑13 NMR signals for aromatic carbons fall between 115 ppm and 140 ppm, while carbonyl carbons resonate near 190 ppm.
Mass Spectrometry
High‑resolution electrospray ionization (ESI) or atmospheric pressure chemical ionization (APCI) techniques provide accurate mass measurements that confirm the exact mass of 200.0541 Da for the C13H10O5 formula. Fragmentation patterns typically involve loss of neutral hydroxyl groups or cleavage of carbonyl bridges.
Infrared Spectroscopy
Characteristic IR absorptions include a broad O–H stretch at 3200–3600 cm⁻¹, a strong C=O stretch near 1700 cm⁻¹, and aromatic C–H stretches between 3000 cm⁻¹ and 3100 cm⁻¹. Additional absorptions may arise from C–O or C–O–C bonds around 1050 cm⁻¹ to 1250 cm⁻¹.
X‑ray Crystallography
Single‑crystal diffraction data provide definitive confirmation of the molecular geometry, including bond lengths and angles. Many C13H10O5 compounds crystallize in orthorhombic or monoclinic systems, with unit cell parameters reflecting the balance between aromatic packing and hydrogen‑bonding interactions.
Natural Occurrence and Biosynthesis
Several naturally occurring substances incorporate the C13H10O5 composition. Plant-derived polyphenols and aromatic ketones are frequently isolated from bark, leaves, and resins. Biosynthetic pathways generally involve the phenylpropanoid pathway, which constructs aromatic rings through shikimate or acetate–malonate precursors. Subsequent enzymatic hydroxylation and oxidation steps introduce the required oxygenated functionalities.
Examples of Natural Products
- Resin acids: Certain resin acids derived from coniferous species contain multiple carboxyl and hydroxyl groups, achieving a C13H10O5 composition when the side chains are truncated.
- Flavonoids: Flavonoid aglycones that have undergone decarboxylation or demethylation may exhibit the thirteen‑carbon skeleton with appropriate oxygenated substituents.
- Anthraquinone derivatives: Secondary metabolites from fungal species often feature anthraquinone cores that can be modified through oxidative pathways to match the C13H10O5 formula.
Applications
Compounds represented by the C13H10O5 formula have garnered interest for a range of technological and pharmaceutical uses. Their aromatic nature and oxygenated functionality provide a versatile platform for interaction with ultraviolet light, radicals, and polymer matrices.
Photoprotective Agents
Many benzophenone derivatives exhibit strong absorption in the UV‑B region, making them suitable as UV filters in cosmetic formulations. The presence of hydroxyl groups enhances photostability by facilitating energy dissipation through non‑radiative decay pathways. The efficacy of these agents is routinely assessed using UV‑visible spectroscopy, with absorption maxima typically around 310 nm to 350 nm.
Antioxidants
Phenolic and carbonyl groups in C13H10O5 compounds contribute to radical scavenging ability. These molecules can donate hydrogen atoms to free radicals, terminating chain reactions in biological and industrial contexts. Standard assays such as the DPPH radical reduction and ABTS⁺ decolorization methods quantify antioxidant capacity, often yielding values comparable to those of well‑known antioxidants like quercetin.
Medicinal Chemistry
Owing to their structural resemblance to biologically active molecules, benzophenone derivatives with multiple oxygen substituents have been explored as enzyme inhibitors and anti‑inflammatory agents. In vitro studies indicate inhibition of cyclooxygenase and lipoxygenase pathways, with potential implications for the treatment of pain and inflammation. Structural modifications that enhance solubility and reduce cytotoxicity are key areas of research.
Polymer Stabilization
Oxygenated aromatic ketones function as stabilizers for polymers exposed to UV light and thermal stress. They act as absorbing chromophores that prevent chain scission in materials such as polyvinyl chloride and polyethylene. Their inclusion in polymer blends is monitored through accelerated aging tests, which assess changes in mechanical properties and discoloration over time.
Environmental Impact and Safety
The environmental fate of C13H10O5 compounds depends largely on their chemical stability and biodegradability. Phenolic and aromatic structures can accumulate in aquatic systems, potentially disrupting endocrine function in organisms. Regulatory agencies classify these substances as hazardous, requiring careful handling, containment, and disposal procedures. Comprehensive risk assessments involve evaluating acute toxicity, skin irritation potential, and phototoxicity using standardized protocols.
Analytical Determination
Accurate quantification of C13H10O5 compounds in complex matrices employs a combination of chromatographic and spectrometric techniques. High‑performance liquid chromatography (HPLC) coupled with UV detection is the most common method for separating isomeric species. Complementary techniques such as gas chromatography–mass spectrometry (GC‑MS) and liquid chromatography–mass spectrometry (LC‑MS) provide detailed mass spectral data that confirm molecular weights and fragmentation patterns.
Quantitative Methods
- Calibration curves: Standard solutions of known concentration generate linear responses across a range of 0.1 mg mL⁻¹ to 10 mg mL⁻¹.
- Internal standards: Deuterated analogs of the target compound serve as internal standards to correct for matrix effects and instrument variability.
- Method validation: Parameters such as accuracy, precision, limit of detection, and limit of quantification are established according to regulatory guidelines.
Summary
The C13H10O5 molecular formula encapsulates a rich set of aromatic and oxygenated organic molecules. These compounds are characterized by high unsaturation, diverse functional groups, and a range of physicochemical properties that facilitate their use in photoprotection, antioxidant activity, pharmaceutical development, and polymer stabilization. Advances in synthetic methodology and spectroscopic characterization continue to expand the repertoire of accessible isomers, offering new opportunities for both applied and fundamental research.
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