Kristalne strukture položajnih izomerov indolkarboksilne kisline

Pajek, Anja (avtor), Počkaj, Marta (mentor)

Položajni izomeri indolkarboksilne kisline in njihovi derivati se zaradi raznolikih lastnosti in učinkov uporabljajo na različnih področjih, še posebno kot intermediati v farmaciji, elektrokemiji, agrokemiji, znanosti o materialih itd. Kljub pomembnosti in pogostosti njihove uporabe pa večina v literaturi še nima opisane kristalne strukture. V magistrskem delu smo zato z uporabo rentgenske difrakcije na monokristalu in elektronske difrakcije analizirali komercialne vzorce položajnih izomerov indolkarboksilne kisline, preučili njihovo zlaganje ter izvedli tudi analizo Hirshfeldovih površin s pomočjo programa CrystalExplorer. Položajne izomere smo analizirali tudi z več različnimi metodami karakterizacije, in sicer z rentgensko praškovno difrakcijo, jedrsko magnetno resonanco, termogravimetrično analizo in diferenčno dinamično kalorimetrijo. Strukturi I2CA in I7CA smo zaradi primerne velikosti in kvalitete kristalov določili z rentgensko difrakcijo na monokristalu, I4CA in I6CA pa z elektronsko difrakcijo. Ugotovili smo, da imata izomera I4CA in I2CA po dve polimorfni obliki. Zaradi nečistosti izomera I5CA smo njegovo podrobnejšo analizo v tem magistrskem delu izpustili. Vsi položajni izomeri ICA se zlagajo v zamaknjene vzporedne plasti, vsi razen polimorfne oblike I4CA P21/c pa vsebujejo še drugo, identično plast, ki glede na prvo leži pod določenim kotom. Med sabo se povezujejo z različno močnimi π…π, C–H…π in C–H…H–C interakcijami. Polimorfni obliki I2CA sta edini, ki se v isti ravnini povezujeta v motiv R_2^2 (9), v cikcakast vzorec, vsi ostali pa v centrosimetrične dimere v motiv R_2^2 (8). Ti izomeri z izjemo I7CA tvorijo še dodatno N–H…O vodikovo vez. S pomočjo izvedenih analiz smo ugotovili, da sprememba položaja karboksilne skupine na indolnem obroču zelo vpliva na zlaganje molekul v kristalih ter na prisotnost in količino medmolekulskih interakcij, posledično pa tudi na ostale lastnosti položajnih izomerov.

• Jezik: Slovenski jezik
• Ključne besede: položajna izomerija, indolkarboksilne kisline, rentgenska difrakcija na monokristalu, 3D elektronska difrakcija, analiza Hirshfeldovih površin
• Vrsta gradiva: Magistrsko delo/naloga
• Organizacija: FKKT - Fakulteta za kemijo in kemijsko tehnologijo
• Leto izida: 2026
• PID: 20.500.12556/RUL-186615
• Datum objave v RUL: 03.09.2026

Sekundarni jezik

• Jezik: Angleški jezik
• Naslov: Crystal structures of positional isomers of indolecarboxylic acid

Izvleček

Positional isomers of indolecarboxylic acid and their derivatives are used in various fields due to their diverse properties and effects, especially as intermediates in pharmacy, electrochemistry, agrochemistry, materials science, etc. However, despite importance and frequency of their use, the crystal structures of most of these compounds have not yet been described in the literature. In this master’s thesis, we therefore analyzed commercial compounds of positional isomers of indolecarboxylic acid using single-crystal X-ray diffraction and electron diffraction, examined their packing, and also performed Hirshfeld surface analysis using the CrystalExplorer software. We also analyzed the positional isomers using several different characterization methods, namely X-ray powder diffraction, nuclear magnetic resonance, thermogravimetric analysis and differential scanning calorimetry. Due to the suitable size and quality of the crystals, we determined structures of I2CA and I7CA using single-crystal X-ray diffraction, while I4CA and I6CA were measured by electron diffraction. We found that the I4CA and I2CA isomers each form two polymorphic forms. Due to the impurities in isomer I5CA, its more detailed analysis has been omitted in this master’s thesis. All positional isomers of ICA stack into offset parallel layers; all except I4CA P21/c also contain a second, identical layer that lies at a specific angle to the first. They are linked to one another by π…π, C–H…π, and C–H…H–C interactions of varying strengths. The two polymorphic forms of I2CA are the only ones that in the same plane assemble into a R_2^2 (9) motif, in a zigzag pattern, while all others form centrosymmetric dimers in a R_2^2 (8) motif. With the exception of I7CA, these isomers form an additional N–H…O hydrogen bond. Based on acquired data, we determined that a change in the position of the carboxylic group on the indole ring has a visible effect on the arrangement of molecules in a crystal, on the presence and extent of intermolecular interactions, and consequently also on the other properties of the positional isomers.

• Ključne besede: positional isomerism, indolecarboxylic acids, single-crystal X-ray diffraction, 3D electron diffraction, Hirshfeld surface analysis