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There are three major classes of halogenated organic compounds. What are they?
- alkyl halide: halogen atom bonded to one of the sp3 hybrid carbon atoms of an alkyl group
- vinyl halide: halogen atom bonded to one of the sp2 hybrid carbon atoms of an alkene
- aryl halide: halogen atom bonded to one of the sp2 hybrid carbon atoms of an aromatic ring
Why is the chemistry of vinyl halides and aryl halides different from that of alkyl halides?
because their bonding and hybridization are different
The carbon-halogen bond in an alkyl halide is polar because __.. Most reactions of alkyl halides result from what?
By serving as a __, the halogen can be __ from the alkyl halide, or it can be __ by a wide variety of functional groups. This versatility allows _ to serve as __ in the synthesis of many other functional groups.
- halogen atoms are more electronegative than carbon atoms
- breaking this polarized bond
- leaving group
- replaced (substituted for)
- alkyl halides
There are two ways of naming alkyl halides. The __ treats an alkyl halide as an __ with a __ substitent. The result is a systematic __ name.
Common or trivial names are constructed by naming the __ and then the __. This is the origin of the term __.
- IUPAC nomenclature
- alkyl group
- halide (ex: isopropyl bromide)
- alkyl halide
A compound of formula CH2X2 is called a __. A compound of formula CHX3 is called a __, and CX4 is called a __.
X= the halogen
- methylene halide
- carbon tetrahalide
Alkyl halides are classified according to the __.
If the halogen-bearing C is bonded to one carbon atom , it is __ and the alkyl halide is a __.
If two carbons are bonded to the halogen-bearing carbon, it is __ and the compound is a __. A __ has three other C atoms bonded to the halogen-bearing carbon atom. If the halogen-bearing carbon atom is a __ (bonded to no other carbon atoms), the compound is a __.
- nature of the carbon atom bonded to the halogen
- primary halide
- secondary halide
- tertiary halide
- methyl group
- methyl halide
A __ has the two halogen atoms bonded to the same carbon. A __ has the two halogens bonded to adjacent carbon atoms.
- geminal dihalide
- vicinal dihalide
Alkyl halides are used primarily as __.
Many syntheses use alkyl halides as __. The conversion of alkyl halides to __ is important for organic synthesis.
The __ are fluorinated haloalkanes that were developed to replace ammonia as a refrigerant gas.
Low boiling reons were once used as __ that were added to a plastic to vaporize adn form a froth that hardens into a plastic foam.
- industrial and household solvents
- starting materials for making more complex molecules
- organometallic reagents (compounds containing C-metal bonds)
- freons (chlorofluorocarbons)
- foaming agents
Alkyl halides have contributed to human health throguh their use as __.
In an alkyl halide, the halogen atom is bonded to an __. The halogen is __ than carbon, and teh C-X bond is __ with a __ on carbon and a __ on the halogen.
Dipole moments are given in __.
The electronegativities of the halogens __.
- sp3 hybrid carbon atom
- more electronegative
- partial positive charge
- partial negative charnge
- increase in the order I<Br<Cl<F
The carbon-halogen bond lengths increases as what?
the halogen atoms become bigger int he order C-F < C-Cl <C-Br < C-CI
How donbond lengths and electronegativity effects opose each other?
What is the overall order?
the harger halogens have longer bonds but weaker electronegativities
this leads to C-I< C-Br <C-F <C-Cl
What is a molecular dipole moment?
vector sum of hte individual bond dipole moments that aren't easy to predict because they depend on bond angles and other factors
Two types of intermoolecular forces influence the BP of alkyl halides. What are they?
- London force: strongest in alkyl halides (surface attractions)
- larger surface area= larger London attractions--> higher BP
- dipole-dipole attractions
Molecules with higher __ generally have higher BP because tehy are __, and they have greater surface area. The surface areas of the alkyl halides vary with the surface areas of halogens.
- heavier (and therefore slower moving)
We can get an idea of the relative surface areas of halogen atoms by considering their __.
van der Waals radii
The other halogens are considerably larger than __, giving them more surface area and raising the __ of their alkyl halides. With
__ and __ are less dense than water. __ with two or more chlorine atoms are denser than water, and all __ and __ are denser than water.
- alkyl fluorides
- alkyl chlorides x2
- alkyl bromides
- alkyl iodides
__ is rarely an effective method for the synthesis of alkyl halides.It usually produces mixtures of products because there are different kinds of hydrogen atoms that can be __. More than one halogen atom may react, giving multiple __.
- free-radical halogenation
In industry, free radical halogenation is sometimes useful because what?
In a lab, however, we need a good yield of one particular product. Free-radical halogenation provides what?
- the reagents are cheap, the mixtures of products can be separated by distillation, and each of the individual products is sold separately
- good selectivity and yield
Formation of dichlorides and trichlorides is possible, but these side reactions are controlled by usign what?
only a small amount of chlorine adn an excess of cyclohexane
__ is highly selective and it gives good yields of products that have one type of hydrogen atom that is more reactive than the others.
free radical bromination
__ has only one tertiary H atom, and this is hte one preferentially abstracted to give a tertiary free radical. In general, however, we are not inclined to use __ in the lab because of the numerous products.
- free radical halogenation
__ can be carried out in a selective manner. An __ position is a carbon atom next to a __. __ are stabilized by __ with the =, allowing the charge or radical to be delocalized.
- free-radical bromination of alkenes
- allylic carbon carbon double bond
- allylic intermediates
If there is an __, the __ is usually rhe more stable of the radicals that might be formed.
- allylic hydrogen
- allylic radical
The mechanism is similar to other free-radical halogenations. A bromine radical abstracts an __ to give a __. This radical reacts with Br2, regenerating a bromine radical that continues the chain reaction.
- allylic hydrogen atom
- resonance-stabilized allylic radical
Either end of the __ can react with bromine to give products. The other product results from reaction at the carbon atom that bears the radical in the __ of the __. This second compound is said to be the product of an __.
- resonance-stabilized allylic radical
- second resonance form
- allylic radical
- allylic shift
For efficient allylic bromination, what
a large concentration of bromine must be avoided because bromine can also add to the double bond
__ is often used as the bromine source in free-radical brominaiton sbecuase it cmbines with teh HBr side product to regenerate a constant low concentration of bromine. No additional bromine is needed because most samples of __ contain traces of Br2 to initiate the reaction.
- N-bromosuccinimide (NBS)
__ also works well for brominating __ positions, next to an __.