Chapter 15 - Haloalkanes Flashcards
What are haloalkanes?
Compounds containing the elements, carbon hydrogen, and at least one halogen atom
What bond do haloalkanes have in their structure?
A carbon-halogen bond
What are nucleophiles?
Negative ions, or molecules with a delta- atom, that can donate a lone pair of electrons to form a new covalent bond
What is unique about the carbon-halogen bond?
Halogen atoms are more electronegative than the carbon atom
So the bond is polar
What reactions do primary haloalkanes undergo?
Nucleophilic substitution
What is special about the carbon in the carbon-halogen bond?
The carbon has a slightly positive charge and can attract nucleophiles
What occurs in the hydrolysis of a haloalkane?
The halogen atom is replaced by an -OH group to form an alcohol
What does the rate of hydrolysis of haloalkanes depend on?
Upon the strength of the carbon-halogen bond
e.g. iodoalkanes react the fastest (C-I bond weakest - less energy required to break bond)
e.g. flouroalkanes react the slowest (C-F bond strongest - more energy required to break bond)
What is hydrolysis?
Chemical reaction involving water or aq hydroxide ions
Describe the mechanism of nucleophilic substitution of a haloalkane
OH- ion approaches the delta+ carbon on the opposite side of the molecule from the delta- halogen atom, to minimise repulstion
A lone pair of electrons on the OH- ion is donated to the delta+ carbon atom and a new bond is formed
The carbon-halogen bond breaks by heterolytic fission
The new organic product is an alcohol\
A halide ion is also formed
What is the observation of the hydrolysis of 1-chlorobutane?
A WHITE precipitate of silver chloride forms very slowly
How do we measure the rate of hydrolysis of primary haloalkanes?
Ethanol and aq silver nitrate solution are added to test tubes containing haloalkanes
Test tubes warmed in water bath
Time taken for the ppt.s of silver halid to appear are measured and recorded
What is the observation of the hydrolysis of 1-bromobutane?
A CREAM precipitate of silver bromide forms slower than for 1-iodobutane, but faster than for 1 chlorobutane
What is the observation of the hydrolysis of 1-iodobutane?
A yellow precipitate of silver iodide forms rapidly
