SFRP Synthesis of Acenaphthylene Oligomers and Block Copolymers. Potential Light Harvesting Structures

Ali, Dildar,Ahmed, Zaheer,Dust, Julian M.,Kazmaier, Peter M.,Buncel, Erwin Korean Chemical Society 2011 Bulletin of the Korean Chemical Society Vol.32 No.7

Azo-acenaphthylene oligomers with repeating acenaphthylene units "n" up to 4, 5, 7, 17 and 19 have been prepared successfully using nitroxide mediated Stable Free Radical Polymerization (SFRP). Azo-acenaphthylene oligomers, reversibly end-capped by the stable nitroxide 2,2,6,6-tetramethyl-1-piperidinoxyl (TEMPO), were further reacted via radical addition to 4-(naphthalenemethoxy)styrene monomer for diblock co-polymer formation. Characterization of the oligomers and diblock co-polymers was accomplished using MALDI-MS supported by GPC (Gel Permeation Chromatography) and $^1H$ NMR spectrometry. MALDI-MS afforded definitive results by providing an inter-peak interval of 152 (m/z), corresponding to acenaphthylene monomer, and inter-peak interval of 260 (m/z) for the naphthalenemethoxystyrene monomer unit in block copolymers. Our study opens the way to control the number of repeat units in the oligomers. Further these oligomers can be tailored with various monomers for the formation of block copolymers.

SFRP Synthesis of Acenaphthylene Oligomers and Block Copolymers. Potential Light Harvesting Structures

Dildar Ali,Peter M. Kazmaier,Julian M. Dust,Zaheer Ahmed,Erwin Buncel 대한화학회 2011 Bulletin of the Korean Chemical Society Vol.32 No.7

Azo-acenaphthylene oligomers with repeating acenaphthylene units “n” up to 4, 5, 7, 17 and 19 have been prepared successfully using nitroxide mediated Stable Free Radical Polymerization (SFRP). Azoacenaphthylene oligomers, reversibly end-capped by the stable nitroxide 2,2,6,6-tetramethyl-1-piperidinoxyl (TEMPO), were further reacted via radical addition to 4-(naphthalenemethoxy)styrene monomer for diblock co-polymer formation. Characterization of the oligomers and diblock co-polymers was accomplished using MALDI-MS supported by GPC (Gel Permeation Chromatography) and ^1H NMR spectrometry. MALDI-MS afforded definitive results by providing an inter-peak interval of 152 (m/z), corresponding to acenaphthylene monomer, and inter-peak interval of 260 (m/z) for the naphthalenemethoxystyrene monomer unit in block copolymers. Our study opens the way to control the number of repeat units in the oligomers. Further these oligomers can be tailored with various monomers for the formation of block copolymers.

Alkali metal ion catalysis and inhibition in alkaline ethanolysis of <i>O</i>-Y-substituted-phenyl <i>O</i>-phenyl thionocarbonates: contrasting M⁺ ion effects upon changing electrophilic centre from C=O to C=S

Um, Ik-Hwan,Kang, Ji-Sun,Dust, Julian M. National Research Council 2017 Canadian journal of chemistry Vol.95 No.1

<P> Pseudo-first-order rate constants (kobsd) were measured for nucleophilic substitution reactions of O-Y-substituted-phenyl O-phenyl thionocarbonates (4a-4h) with alkali metal ethoxides (EtOM, M = Li, Na, or K) in anhydrous ethanol at 25.0 ± 0.1 °C. Plots of kobsd vs. [EtOM] exhibited upward curvature for the reaction of O-4-nitrophenyl O-phenyl thionocarbonate (4a) with EtOK in the presence of 18-crown-6-ether (18C6), but showed downward curvature for the reaction with EtOLi, indicating that the reaction is catalyzed by the 18C6-crowned K<SUP>+</SUP> ion, but is inhibited by Li<SUP>+</SUP> ion. The kobsd values were dissected into kEtO− and kEtOM, the second-order rate constant for the reaction with dissociated EtO<SUP>−</SUP> and ion-paired EtOM, respectively. The reactivity of EtOM toward 4a increases in the order EtOLi @@<@@ EtONa @@<@@ EtO<SUP>−</SUP> @@<@@ EtOK @@<@@ EtOK/18C6, which is in contrast to that reported previously for the corresponding reaction of 4-nitrophenyl phenyl carbonate (a C=O analogue of 4a), e.g., EtO<SUP>−</SUP> ≈ EtOK/18C6 @@<@@ EtOLi @@<@@ EtONa @@<@@ EtOK. The reaction mechanism, including the transition-state model and the origin of the contrasting reactivity patterns found for the reactions of the C=O and C=S compounds, are discussed. </P>

Medium effect (water versus MeCN) on reactivity and reaction pathways for the S_NAr reaction of 1-aryloxy-2,4-dinitrobenzenes with cyclic secondary amines

Um, Ik-Hwan,Kim, Min-Young,Dust, Julian M. Canadian Science Publishing 2017 Canadian journal of chemistry Vol.95 No.12

<P> A kinetic study on SNAr reactions of 1-aryloxy-2,4-dinitrobenzenes (1a-1h) with a series of cyclic secondary amines in 80 mol% water - 20 mol% DMSO at 25.0 ± 0.1 °C is reported. The plots of kobsd versus amine concentration curve upward except for the reactions of substrates possessing a strong electron-withdrawing group in the leaving aryloxide with strongly basic piperidine. The curved plots indicate that the reactions proceed through both uncatalytic and catalytic routes. Linear Brønsted-type plots have been obtained for the uncatalyzed and catalyzed reactions of 1-(4-nitrophenoxy)-2,4-dinitrobenzene (1a) with βnuc = 0.84 and 0.78, respectively. The Yukawa-Tsuno plot for the uncatalyzed reactions of 1a-1h with piperidine results in an excellent linear correlation with ρ = 1.66 and r = 0.31. In contrast, rate constants for catalyzed reactions are independent of the electronic nature of the substituent in the leaving group. The current SNAr reactions have been proposed to proceed via a zwitterionic intermediate (MC<SUP>±</SUP>) that partitions to products through uncatalytic and catalytic routes. The catalyzed reaction from MC<SUP>±</SUP> has been concluded to proceed through a concerted mechanism with a six-membered cyclic transition state (TScycl) rather than via a stepwise pathway with a discrete anionic intermediate (MC<SUP>−</SUP>), the traditionally accepted mechanism. Medium effects on the reactivity and reaction mechanism are discussed. Particularly, hydrogen bonding of the amines to water precludes formation of kinetically significant dimers found in some aprotic solvents; no explicit role for water in the catalytic transition state is required or proposed. The specific stabilization of the leaving aryloxides substituted with strong electron-withdrawing groups accounts for the lack of the catalytic pathway in these systems (1a-1c) with piperidine nucleophile. </P>

Kinetic Study on S_NAr Reaction of 1-(Y-Substituted-phenoxy)-2,4-dinitrobenzenes with Cyclic Secondary Amines in Acetonitrile: Evidence for Cyclic Transition-State Structure

Um, Ik-Hwan,Kim, Min-Young,Kang, Tae-Ah,Dust, Julian M. American Chemical Society 2014 Journal of organic chemistry Vol.79 No.15

<P>A kinetic study is reported for S<SUB>N</SUB>Ar reactions of 1-(Y-substituted-phenoxy)-2,4-dinitrobenzenes (<B>1a</B>–<B>1h</B>) with amines in MeCN. The plots of pseudo-first-order rate constant versus amine concentration curve upward, indicating that the reactions are catalyzed by a second amine molecule. The Brønsted-type plots for the reaction of 1-(4-nitrophenyl)-2,4-dinitrobenzene (<B>1a</B>) with secondary amines are linear with β<SUB>nuc</SUB> = 1.10 and 0.85 for the uncatalyzed and catalyzed reactions, respectively, while the Yukawa–Tsuno plots for the reactions of <B>1a</B>–<B>1h</B> with piperidine result in excellent linear correlations with ρ<SUB>Y</SUB> = 1.85 and <I>r</I> = 0.27 for the uncatalyzed reaction and ρ<SUB>Y</SUB> = 0.73 and <I>r</I> = 0.23 for the catalyzed reaction. The catalytic effect decreases with increasing amine basicity or electron-withdrawing ability of the substituent Y in the leaving group. Activation parameters calculated from the rate constants measured at five different temperatures for the catalyzed reaction of <B>1a</B> with piperidine are Δ<I>H</I><SUP>‡</SUP> = 0.38 kcal/mol and Δ<I>S</I><SUP>‡</SUP> = −55.4 cal/(mol K). The catalyzed reaction from a Meisenheimer complex (MC<SUP>±</SUP>) is proposed to proceed through a concerted mechanism with a cyclic transition-state rather than via a stepwise pathway with an anionic intermediate, MC<SUP>–</SUP>. Deuterium kinetic isotope effects provide further insight into the nature of the concerted transition state.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/joceah/2014/joceah.2014.79.issue-15/jo5011872/production/images/medium/jo-2014-011872_0010.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jo5011872'>ACS Electronic Supporting Info</A></P>

Mechanistic Assessment of S_NAr Displacement of Halides from 1-Halo-2,4-dinitrobenzenes by Selected Primary and Secondary Amines: Brønsted and Mayr Analyses

Um, Ik-Hwan,Im, Li-Ra,Kang, Ji-Sun,Bursey, Samantha S.,Dust, Julian M. American Chemical Society 2012 Journal of organic chemistry Vol.77 No.21

<P>Pseudo-first-order rate constants (<I>k</I><SUB>obsd</SUB>) have been measured spectrophotometrically for nucleophilic substitution reactions of 1-X-2,4-dinitrobenzenes (<B>1a</B>–<B>d</B>, X = F, Cl, Br, I) with various primary and secondary amines in MeCN and H<SUB>2</SUB>O at 25.0 ± 0.1 °C. The plots of <I>k</I><SUB>obsd</SUB> vs [amine] curve upward for reactions of <B>1a</B> (X = F) with secondary amines in MeCN. In contrast, the corresponding plots for the other reactions of <B>1b</B>–<B>d</B> with primary and secondary amines in MeCN and H<SUB>2</SUB>O are linear. The Brønsted-type plots for reactions of <B>1a</B>–<B>d</B> with a series of secondary amines are linear with β<SUB>nuc</SUB> = 1.00 for the reaction of <B>1a</B> and 0.52 ± 0.01 for those of <B>1b</B>–<B>d</B>. Factors governing reaction mechanisms (e.g., solvent, halogen atoms, H-bonding interactions, amine types) have been discussed. Kinetic data were also analyzed in terms of the Mayr nucleophilicity parameter for the amines with each aromatic substrate. Provisional Mayr electrophilicity parameter (<I>E</I>) values for 1-X-2,4-dinitrobenzenes have been determined: <I>E</I> = −14.1 for X = F, <I>E</I> = −17.6 for X = Cl and Br, and <I>E</I> = −18.3 for X = I. These values are consistent with the range and order of <I>E</I> values for heteroaromatic superelectrophiles and normal 6-π aromatic electrophiles.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/joceah/2012/joceah.2012.77.issue-21/jo301862b/production/images/medium/jo-2012-01862b_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jo301862b'>ACS Electronic Supporting Info</A></P>

Unexpected medium effect on the mechanism for aminolysis of aryl phenyl carbonates in acetonitrile and H₂O: transition-state structure in the catalytic pathway

Um, Ik-Hwan,Song, Ji-Hyun,Bae, Ae-Ri,Dust, Julian M. National Research Council 2018 Canadian journal of chemistry Vol.96 No.12

<P> Upward curvature in the kinetic plots of pseudo first-order rate constants (kobsd) vs. [amine] for the aminolysis of aryl phenyl carbonates (5a-5j) in MeCN demonstrates that these reactions proceed via a zwitterionic tetrahedral intermediate (T<SUP>±</SUP>) that partitions between catalyzed and uncatalyzed routes to give the products. Yukawa-Tsuno plots for the reactions of 5a-5j with piperidine result in excellent linear correlations with ρY = 4.82 and r = 0.47 for the uncatalyzed reaction versus ρY = 2.21 and r = 0.21 for the catalyzed reaction. Brønsted plots for reactions of 4-(ethoxycarbonyl)-phenyl phenyl carbonate (5f) with a series of cyclic secondary amines exhibit excellent linear correlations with βnuc = 0.87 and 0.58 for the uncatalyzed and catalyzed reactions, respectively. The ΔH<SUP>‡</SUP> and ΔS<SUP>‡</SUP> values are 0.92 kcal/mol and -50.1 cal/mol K, respectively, for the catalyzed reaction of 5f with piperidine. Deuterium kinetic isotope effects found for reactions of 5f with piperidine/deuterated piperidine are 0.84 (uncatalyzed) and 1.42 (catalyzed). Multi-parameter analysis supports a concerted catalytic pathway involving a six-membered cyclic transition state rather than a traditionally accepted stepwise pathway with an anionic intermediate. The current unexpected results, where T<SUP>±</SUP> is the essential central intermediate in this aminolysis, contrast with previous calculation studies that deemed T<SUP>±</SUP> unstable in gas phase or MeCN. </P>

Evidence for a Catalytic Six-Membered Cyclic Transition State in Aminolysis of 4-Nitrophenyl 3,5-Dinitrobenzoate in Acetonitrile: Comparative Brønsted-Type Plot, Entropy of Activation, and Deuterium Kinetic Isotope Effects

Um, Ik-Hwan,Kim, Min-Young,Bae, Ae-Ri,Dust, Julian M.,Buncel, Erwin American Chemical Society 2015 Journal of organic chemistry Vol.80 No.1