Related Experiment Video
Updated: Jul 2, 2026
08:56
Synthesis of 1,2-Azaborines and the Preparation of Their Protein Complexes with T4 Lysozyme Mutants
Published on: March 25, 2017
Favoring heterotrimeric boroxine formation using an internal Lewis base: a computational study
Jeremy Kua1, Charles R Gyselbrecht
1Department of Chemistry and Biochemistry, University of San Diego, 5998 Alcala Park, San Diego, California 92110, USA. jkua@sandiego.edu
The Journal of Physical Chemistry. A
|August 30, 2008
Summary
Designing arylboronic acid monomers with a Lewis base enables favorable formation of heterotrimeric arylboroxines. Computational studies reveal AB2 trimers are most stable, especially with electron-withdrawing groups on the B monomer.
Area of Science:
- Supramolecular Chemistry
- Computational Chemistry
- Organic Synthesis
Background:
- Arylboroxines are cyclic trimers formed from arylboronic acids.
- Controlling the composition of heterotrimeric arylboroxines is challenging.
- Pendant Lewis bases can influence the self-assembly of boronic acids.
Purpose of the Study:
- To investigate the thermodynamic favorability of forming heterotrimeric arylboroxines (AB2, A2B) versus homotrimeric forms (A3, B3).
- To identify structural features that stabilize specific heterotrimeric arylboroxine compositions.
- To explore the impact of substituents on monomeric arylboronic acids on trimer stability.
Main Methods:
- Density functional theory (DFT) calculations using the B3LYP//6-311+G* level of theory.
- Inclusion of implicit solvent effects using the Poisson-Boltzmann model.
- Thermodynamic analysis of different trimer compositions (A3, B3, A2B, AB2, ABC).
Main Results:
- AB2 trimers, featuring one arylboronic acid with a Lewis base (A) and two without (B), are thermodynamically favored over other compositions.
- The stability of AB2 trimers is enhanced by electron-withdrawing substituents (halogens, pi-acceptors) on the B monomer.
- Substituents on the A monomer (with the Lewis base) have a minor impact on trimer energetics.
Conclusions:
- Strategic placement of a pendant Lewis base and electron-withdrawing groups allows for predictable synthesis of stable heterotrimeric arylboroxines.
- The AB2 composition is generally the most stable heterotrimer, offering a route to controlled supramolecular assembly.
- Computational methods provide valuable insights into the design principles for constructing complex arylboroxine architectures.
Related Concept Videos
02:16Lewis Acids and Bases
This lesson delves into Lewis acids and bases in the context of the octet rule for electron-deficient compounds. Here, the concept is discussed, emphasizing the group 13 elements like boron or aluminium. Since group 13 elements possess three valence electrons, they form trivalent compounds with a sextet of electrons and a vacant orbital for the central atom. Consequently, these electron-deficient compounds accept electrons from other species to complete their octet in a chemical reaction. They...
02:33Lewis Acids and Bases
In 1923, G. N. Lewis proposed a generalized definition of acid-base behavior in which acids and bases are identified by their ability to accept or to donate a pair of electrons and form a coordinate covalent bond.
A coordinate covalent bond (or dative bond) occurs when one of the atoms in the bond provides both bonding electrons. For example, a coordinate covalent bond occurs when a water molecule combines with a hydrogen ion to form a hydronium ion. A coordinate covalent bond also results when...
A coordinate covalent bond (or dative bond) occurs when one of the atoms in the bond provides both bonding electrons. For example, a coordinate covalent bond occurs when a water molecule combines with a hydrogen ion to form a hydronium ion. A coordinate covalent bond also results when...
02:55Exceptions to the Octet Rule
Many covalent molecules have central atoms that do not have eight electrons in their Lewis structures. These molecules fall into three categories:
02:36Regioselectivity and Stereochemistry of Hydroboration
A significant aspect of hydroboration–oxidation is the regio- and stereochemical outcome of the reaction.
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn stereochemistry.
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn stereochemistry.
03:08Hydroboration-Oxidation of Alkenes
In addition to the oxymercuration–demercuration method, which converts the alkenes to alcohols with Markovnikov orientation, a complementary hydroboration-oxidation method yields the anti-Markovnikov product. The hydroboration reaction, discovered in 1959 by H.C. Brown, involves the addition of a B–H bond of borane to an alkene giving an organoborane intermediate. The oxidation of this intermediate with basic hydrogen peroxide forms an alcohol.
03:08Rate-Determining Steps
Relating Reaction Mechanisms
In a multistep reaction mechanism, one of the elementary steps progresses significantly slower than the others. This slowest step is called the rate-limiting step (or rate-determining step). A reaction cannot proceed faster than its slowest step, and hence, the rate-determining step limits the overall reaction rate.
The concept of rate-determining step can be understood from the analogy of a 4-lane freeway with a short-stretch of traffic-bottleneck caused due to...
In a multistep reaction mechanism, one of the elementary steps progresses significantly slower than the others. This slowest step is called the rate-limiting step (or rate-determining step). A reaction cannot proceed faster than its slowest step, and hence, the rate-determining step limits the overall reaction rate.
The concept of rate-determining step can be understood from the analogy of a 4-lane freeway with a short-stretch of traffic-bottleneck caused due to...