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An unknown molecule A has 4 signals in the 1 H NMR spectrum. Which of the following corresponds to molecule A . How many nonequivalent protons does the following structure have? . 4.
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An unknown molecule A has 4 signals in the 1H NMR spectrum. Which of the following corresponds to molecule A
How many nonequivalent protons does the following structure have? 4
Reading from left to right, what multiplicity would be found for the three nonequivalent sets of protons in the 1H NMR spectrum of the following compound? d, d, s
Give the number of lines in the coupling pattern for each type of hydrogen. 2, 7, 7, 2
Introduction Homolytic bond cleavage leads to the formation of radicals(also called free radicals) Radicals are highly reactive,, short lived species Single headed arrows are used to show the movement fo single electrons. Production of Radicals Homolysis of relatively weak bonds such as O-O and X-X bonds can occur with the addition of energy in the form of heat or light.
Carbon radicals are categorized as primary (1°), secondary (2°) and tertiary (3°) based on the number of attached R groups. 1° 2° 3° A carbon radical is sp2 hybridized with a trigonal planar geometry with the unpaired electron in the unhybridized p orbital. Bond dissociation energy is used as a measure of radical stability.
Two different radicals can be formed with the cleavage of a C-H bond. Basically, the more alkyl groups attached to the radical carbon the more stable it is. Also the more stable the radical, the less energy it takes to break the C-H bond.
What type of radical are each of the following? • • • 3° 1° 2° Of these three radicals, which is the most stable? •
Radical Reactions of Alkanes Abstraction of a H from a C-H bond in which one electron is sued to form H-X while the other is left on the new alkyl radical. • • A radical can also add to a alkene by adding onto a double bond and leaving the other carbon that was part fo the double bond as a radical. • •
Radicals are highly reactive and unstable and usually react quickly with a sigma or pi bond. However sometimes they can react with another radical. • • When oxygen, a diradical, is present it acts as a radical inhibitor or scavenger. Meaning it prevents the radical from attacking any alkanes or alkenes. • • • •
In the presence of heat and light, alkanes and halogens will react to form alkyl halides.
Predict the products from the monobromination of the foloowing compound?
Step 1 - Initiation • Step 2 – Propagation • • • • Step 3 - Termination
In each step of the propagation a bond is broken and formed. And because the overall step has a -H it is exothermic. Step 1 is called the rate determini g step because it is higher in energy.
Transition States Cl----H----CH2CH3 Cl---Cl---- CH2CH3
There are 6 Methyl H’s and 2 Methylene H s. Based on this, the ratio fo the two products should be 3:1(primary to secondary). However, the ratio is 1:1. The more stable the radical being formed is, the easier it is to cleave the C-H bond.
Chlorination is faster and nonselective. This is due to it’s rate determining step being exothermic. Bromination is slower and chooses the most stablew radical. This due to it’s rate determining step being endothermic.
Halogenation is useful in the formation of alkenes. An elimination in the presence of a strong base is responsible for the formation of the alkene.
Conversion of the alkene to an alcohol via nucleophillic substitution is an extension of the utility of radical halogenation.
Oxymercuration-demercuration of an alkene results in the formation of an ether.
Radical halogenations give a racemic mixture of pRodcuts when possible. This halogenation of an achiral compound results in 3 products. A primary and secondary alkyl halide. The secondary halide exist as a pair of enantiomers due to the creation of a stereogenic center upon halogenation.
enantiomers diastereomers
Only achieve enantiomers or diastereomers if the halogenation takes place at a stereogenic center.
