T1- p Block LP6 Flashcards
What are noble gases?
Group 18 elements
What is the structure of XeF6? (Without a diagram)
14 e- gaseous structure is a monocapped octahedron i.e. with a lone pair projecting from one face. one pair distorts the octahedron by pushing back three of the F- ligands. Structure is fluxional and lone pair shifts from face to face- average of all eight structures.
What is the structure of XeF4?
Solution state structure: 129Xe NMR spectrum shows centre of 25 line spectrum arising from coupling of Xe nucleus with 24 equivalent F atoms – fluxionality
What is the structure of XeF6?
Solid state structure: Best represented as an [XeF5] + cation and a F- anion i.e. [XeF5]+ F -. One of the F’s in each molecule is partially dissociated, bridging between the [XeF5]+ cations to form a tetramer
What is fluxionality?
Lone pair exchanging position between all faces of the structure.
Describe xenon fluorides.
They are all colourless and are volatile solids due to the very weak Xe-F bonds. They compounds can be used to fluorinate other molecules, with the fluorinating strength increasing as the number of halogen atoms bound to the xenon atom increases.
What type of structures do you form when you react silsesquioxanes (RSiCl3 where R is an alcohol group)?
It forms many ring, cluster and polymeric structures determined kinetically.
Silsesquioxanes can be formed by hydrolysis of a trichlorosilane, RSiCl3. Which of the following is the most significant driving force for the reaction?
The difference in Si-O and Si-Cl bond strengths. During the reaction of RSiCl3 with 3 H2O, 3 Si-Cl bonds are broken and replaced by Si-O bonds. This results in formation of silsesquioxanes
Is borazine consedered to be very aromatic?
No, because nitrogen is a lot more electronegative (3.04) and smaller (0.70 Å) than boron (2.04, 0.88 Å). So, more localised charges than benzene in structures that are in resonance with the neutral representation
Does boraphosphabenzene considered to be very aromatic?
Yes, because delocalisation of electrons. The central six-membered ring is planar boron-carbon and phosphorous-carbon bonds are essentially in the plane of the central ring, the B-P bonds are equidistant and about 1.84 Å in length.
What is carbene?
It is a divalent carbon centre, usually sp2 hybridised, with a lone pair of electrons.
What are the two ways lone pair in carbene can be arranged?
With spins paired or as 2 unpaired electrons. These 2 different configurations are known as singlet and triplet carbenes.
What happens if two triplet carbenes react?
Alkene will form.
What happens if two singlet carbenes react?
The lone pair of electrons on one carbene will repel the lone pair on a second singlet carbene, meaning the usual planar alkene is less likely to form.
What happens when 2 silylene species react?
Double fond is formed but in a different way than two triplet carbenes react. The singlet state has its lone pair of electrons in a sp2 hybrid orbital. Two of these species interact as a Lewis acid-base pair, with the lone pair of one singlet silylene accepted by an empty unhybridised p-orbital on another.
