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Haloalkanes
Haloalkanes
Haloalkanes are hydrocarbon compounds in which the functional group is a halogen.
Haloalkanes are hydrocarbon compounds in which the functional group is a halogen.
They are normally named with the halogen as a side chain / group of an alkane, eg chloropropane (CH₃CH₂CH₂Cl), 1,3-diiodobutane (CH₂BrCH₂CHBrCH₃).
They are normally named with the halogen as a side chain / group of an alkane, eg chloropropane (CH₃CH₂CH₂Cl), 1,3-diiodobutane (CH₂BrCH₂CHBrCH₃).
Like alcohols they are classified as 1°, 2° and 3°
Like alcohols they are classified as 1°, 2° and 3°
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haloalkanes - 1°, 2° and 3°
haloalkanes - 1°, 2° and 3°
haloalkanes - physical properties
haloalkanes - physical properties
The bond between the C and the halogen (X), be it F, Cl, Br, is polar due to the difference in electronegativity. Iodine and Carbon have the same electronegativity (2.5). This means most haloalkanes are polar which affects their physical properties
The bond between the C and the halogen (X), be it F, Cl, Br, is polar due to the difference in electronegativity. Iodine and Carbon have the same electronegativity (2.5). This means most haloalkanes are polar which affects their physical properties
solubility
solubility
Haloalkanes are not soluble in water, even though they contain a polar bond. In simple terms this is because the polar bond is not 'strong' (polar) enough to break apart the hydrogen bonding existing between the water molecules. In effect the energy required to break apart the dipole-dipole attractions within the haloakane and the hydrogen bonds in water is greater than the energy that would be released when new attractive forces are set up between the haloalkane and water, thus making it not happen.
Haloalkanes are not soluble in water, even though they contain a polar bond. In simple terms this is because the polar bond is not 'strong' (polar) enough to break apart the hydrogen bonding existing between the water molecules. In effect the energy required to break apart the dipole-dipole attractions within the haloakane and the hydrogen bonds in water is greater than the energy that would be released when new attractive forces are set up between the haloalkane and water, thus making it not happen.
boiling point
boiling point
Due to their polarity they have higher melting and boiling points than the corresponding alkanes. However they are unable to hydrogen bond to each other so their melting and boiling points are less than alcohols, amines and carboxylic acids with the same number of carbons.
Due to their polarity they have higher melting and boiling points than the corresponding alkanes. However they are unable to hydrogen bond to each other so their melting and boiling points are less than alcohols, amines and carboxylic acids with the same number of carbons.
As can be seen with the boiling point increases with increasing size of the molecule due to increasing amounts of the weak temporarily induced dipoles, and the boiling point of the iodoalkanes is higher than the bromides which are higher than the chloros - the trend increases down the group, due to increasing number of electrons and thus stronger induced dipole-dipole forces.
As can be seen with the boiling point increases with increasing size of the molecule due to increasing amounts of the weak temporarily induced dipoles, and the boiling point of the iodoalkanes is higher than the bromides which are higher than the chloros - the trend increases down the group, due to increasing number of electrons and thus stronger induced dipole-dipole forces.
Even though the strength of the polar bond decreases down the group (remember F is the most electronegative element with a value of 4.0) the boiling point increases. This must mean that the increasing amount of electrons leading to larger temporarily induced dipole -dipole forces has a greater effect on boiling point that the permanent dipoles.
Even though the strength of the polar bond decreases down the group (remember F is the most electronegative element with a value of 4.0) the boiling point increases. This must mean that the increasing amount of electrons leading to larger temporarily induced dipole -dipole forces has a greater effect on boiling point that the permanent dipoles.
haloalkanes - reactions
haloalkanes - reactions
Halogens are nucleophiles, so undergo nucleophilil substitution.
Halogens are nucleophiles, so undergo nucleophilil substitution.
Nucleophiles donates an electron pair to an electrophiles to form a chemical bond in relation to a reaction.
Nucleophiles donates an electron pair to an electrophiles to form a chemical bond in relation to a reaction.
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