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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
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Why is the chemistry of vinyl halides and aryl halides different from that of alkyl halides?
because their bonding and hybridization are different
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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
- eliminated
- replaced (substituted for)
- alkyl halides
- intermediates
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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
- alkane
- halo-
- haloalkane
- alkyl group
- halide (ex: isopropyl bromide)
- alkyl halide
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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
- haloform
- carbon tetrahalide
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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
- primary halide
- secondary
- secondary halide
- tertiary halide
- methyl group
- methyl halide
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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
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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
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Alkyl halides have contributed to human health throguh their use as __.
insecticides
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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
- polarized
- partial positive charge
- partial negative charnge
- debyes
- increase in the order I<Br<Cl<F
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The carbon-halogen bond lengths increases as what?
the halogen atoms become bigger int he order C-F < C-Cl <C-Br < C-CI
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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
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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
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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
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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.
- MW
- heavier (and therefore slower moving)
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We can get an idea of the relative surface areas of halogen atoms by considering their __.
van der Waals radii
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The other halogens are considerably larger than __, giving them more surface area and raising the __ of their alkyl halides. With
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__ 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
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__ 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
- abstracted
- substitutions
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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
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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
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__ 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
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__ 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.
- isobutane
- free radical halogenation
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__ 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
- resonance
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If there is an __, the __ is usually rhe more stable of the radicals that might be formed.
- allylic hydrogen
- allylic radical
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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
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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
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For efficient allylic bromination, what
a large concentration of bromine must be avoided because bromine can also add to the double bond
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__ 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)
- NBS
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__ also works well for brominating __ positions, next to an __.
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