Positron emission tomography (PET) is a medical imaging technique that produces
ID: 535073 • Letter: P
Question
Positron emission tomography (PET) is a medical imaging technique that produces a threedimensional picture of functional processes in the body, such as the brain uptake of glucose. PET imaging requires the introduction of [18F]-fluorine (a radioactive isotope of fluorine) into molecules and can be achieved by several routes, such as the following (Tetrahedron Lett. 2003, 44, 9165–9167):
(a) Identify the hybridization for every heteroatom (atom other than C or H) in the three compounds. Note: In this problem, none of the lone pairs have been drawn.
(b) Predict the bond angle of each C-N-C bond in the product.
(c) Identify the type of atomic orbital(s) that contain the lone pairs on the oxygen atom in the product.
H 18 F-C-C-Br H H H H-C H H N-C-C-O-H H-C H H H H H H C H H 18 F-C-C-N-C-C-O-H H H H H HTI H BrExplanation / Answer
Compound 1. 1-Bromo-2-fluoroethane
It has two heteroatoms, Br, and F
Br electronic configuration is [Ar] 4s2 4p5 ------- hybridization is sp3 and the structure has 3 lone pairs and one bond pair.
F electronic configuration is [He] 2s2 2p5 ------- hybridization is sp3 and the structure has 3 lone pairs and one bond pair.
Reactant 2. 2-(dimethylamino)ethanol
Two heteroatoms are present N and O
the electronic configuration of N is [He] 2s2 2p3 ------- hybridization is sp3 and the structure has 1 lone pairs and 3 bond pair.
the electronic configuration of O is [He] 2s2 2p4 ------- hybridization is sp3 and the structure has 2 lone pairs and 2 bond pair.
Product
Product has 3 heteroatoms, F, O and N
F electronic configuration is [He] 2s2 2p5 ------- hybridization is sp3 and the structure has 3 lone pairs and one bond pair.
the electronic configuration of O is [He] 2s2 2p4 ------- hybridization is sp3 and the structure has 2 lone pairs and 2 bond pair.
the electronic configuration of N+ is [He] 2s2 2p2
on the excited state [He] 2s1 2p3 ------- hybridization is sp3 and the structure has 0 lone pairs and 4 bond pairs.
b). In product the hybridization is sp3 and the structure has 0 lone pairs. Thus structure is tetrahedron with an angle of 109o28'
c) the electronic configuration of O is [He] 2s2 2p4 ------- hybridization is sp3 and the structure has 2 lone pairs and 2 bond pair.
on splitting the p orbitals
[He] 2s2 2px2 , 2py1 , 2pz1 ....Thus 2pz1 and 2py1 orbitals participate in sigma bonding and lone pairs exist in 2s2 2px2