Main Group Chemistry (CHM303) Quiz

Main Group Chemistry (CHM303)

• Course taught by Dr. Kuduva R. Vignesh
• Email: [email protected]

Lower Halides of Boron (B₂X₄)

• Boron dihalides (B₂X₄) exist in various forms (solid, liquid, gas)
• Melting and boiling points vary depending on the halide (X)
• Thermal stability follows a predictable pattern related to π-bonding between X and B.
• Structures and bonding are described in terms of planar (D2h) and staggered (D2d) geometries.
• Isoelectronic with C₂O₄²⁻ and N₂O₄.

Simple Trihalides of Heavier Group 13 Elements

• Trifluorides of Al, Ga, In, and Tl are non-volatile solids.
• Preparation often involves fluorination of the metal or its compounds with F₂.
• Aluminum trifluoride (AlF₃) can also be prepared by reacting aluminum oxide with hydrogen fluoride.
• Each trifluoride has a high melting point and an infinite structure.
• AlF₃ has octahedral Al centers surrounded by 6 F atoms.

Reactivity

• Water vigorously reacts with solid aluminum chloride, leading to hydrolysis.
• In coordinating solvents (like diethyl ether), aluminum chloride forms adducts.
• Interactions like hydrogen bonding are observed in the solid state of aluminum halides.
• The Tl(III) halides are less stable than those of earlier group 13 elements.

Lower Oxidation State Al, Ga, In, and Tl Halides

• Aluminum (I) halides are formed through reactions involving Al(III) halides and Al metal at high temperatures (1270 K).
• Other techniques include reacting the metal with HCl at high temperatures.
• Gallium(I) chloride and bromide are formed at elevated temperatures in specific conditions.
• Tl(I) halides are more stable than Tl(III) halides.

Molecular Species Containing B-N or B-P Bonds

• Formation of B-N single bonds in adducts, involves symmetric cleavage of B₂H₆.
• Molecular compounds with boron-nitrogen multiple bonds exist.
• Boron nitride (BN) has a layered structure similar to graphite.
• Borazine (B3N3H6) is isoelectronic and isostructural with benzene.

Molecular Species Containing B-N or B-P Bonds. Preparation

• Borazine is prepared through specific reactions, typically B2H6 with ammonia.
• Borazine's reactivity contrasts sharply with that of benzene.

Molecular Species Containing B-N or B-P Bonds. Properties

• Borazine is a colorless liquid with aromatic odor and properties resembling benzene.
• Borazine's BN distances and charge distribution are similar to benzene, but with variations affecting nucleophilic and electrophilic attack.

Nomenclature

• Boranes are named based on the number of boron and hydrogen atoms, and if an anion.

• Further descriptors (e.g., closo-, nido-, arachno-) are often used.

• Polyhedral skeletal electron pair theory (adopted rules) are used.

• Wade's rules are used for categorizing and predicting the structures of boranes and carboranes.

Polyhedral Borane Cluster Compounds

• Different types of bonds are found depending on the compound and their configurations (examples shown)
• Specific naming and numbering systems for boranes are used (styx).

Borazine, H3B3O3

• Boroxine is isoelectronic with benzene.
• It can be produced by oxidizing B₂H₆ or related compounds.
• It's less stable than substituted boroxines, which are solid at room temperature.
• Boroxine is planar but has less π-electron delocalization compared to borazine.
• Trimethylboroxine and triphenylboroxine exist in equilibrium with their respective boronic acids.

Phosphorus Analogue of Borazine

• The phosphorus analogue of borazine, B3P3H6, deviates slightly from planarity.
• The B3P3R6 rings can form π-complexes with transition metal carbonyl fragments.
• The structure of B₃P₃ is planar with equal B-P bond lengths.

Dewar Benzene

• A bicyclic isomer of benzene with considerable strain energy.
• The carbons where the rings join are bonded to four atoms, leading to a non-planar structure, differing from the typical structure of benzene.

Hetero-boranes

• Many derivatives of boranes containing other main group atoms are also known.
• These heteroboranes can be classified using the same principles as for typical boron hydrides, adjusting for the valence electrons of the heteroatom.

Nomenclature of Other atoms

• When classifying other atoms, they are substituted as BH₁, BH₂, or BH₃ to classify more properly.

Test your knowledge on the properties and structures of boron halides and heavier group 13 trihalides with this quiz. Covering topics from geometries to reactivity, this quiz is ideal for students of Dr. Vignesh's chemistry course. Challenge yourself to recall essential concepts and their chemical implications.