Vriti Edustore
Home »
Ask & Discuss
»
Chemistry
« Back to Discussion
Organic Chemistry
28 Jan 2007 12:06:09 IST
0 People liked this
5
673
alkanes questions information
Engineering Entrance
,
Medical Entrance
,
AIPMT
,
JEE Main
,
AIIMS
,
JEE Advanced
,
Chemistry
,
Organic Chemistry
SIR,
COULD YOU PLEASE SEND ME IMPORTANT QUESTION PATTERNS AND TOPICS RELATED TO ALKANES e.g IUPAC NOMENCLATURE OR ITS WAYS OF PREPARATION ..
IT WOULD BE VERY GRAYTEFUL TO YOU...
OTHER MEMBERS CAN ALSO MAIL ME AT aakash_aastha@yahoo.com.
Thank you
Comments (5)
smriti.mathur
Forum Expert
Joined: 27 Dec 2006
Posts: 423
30 Jan 2007 12:26:16 IST
Like
0 people liked this
Important topics in alkanes are their methods of preparation, isomerism exhibited by them, their IUPAC nomenclature, and mechanisms of reactions like Kolbe's electrolytic method, Wurtz reaction, decarboxylation, and free radical mechanism of halogenation of alkanes.
Reply
30 Jan 2007 12:34:00 IST
Like
1 people liked this
Alkanes
Hydrocarbons having no double or triple bond functional groups are classified as alkanes or cycloalkanes, depending on whether the carbon atoms of the molecule are arranged only in chains or also in rings. Although these hydrocarbons have no functional groups, they constitute the framework on which functional groups are located in other classes of compounds, and provide an ideal starting point for studying and naming organic compounds. The alkanes and cycloalkanes are also members of a larger class of compounds referred to as aliphatic. Simply put, aliphatic compounds are compounds that do not incorporate any aromatic rings in their molecular structure.
The following table lists the IUPAC names assigned to simple continuous-chain alkanes from C-1 to C-10. A common "ane" suffix identifies these compounds as alkanes. Longer chain alkanes are well known, and their names may be found in many reference and text books. The names methane through decane should be memorized, since they constitute the root of many IUPAC names. Fortunately, common numerical prefixes are used in naming chains of five or more carbon atoms.
The following table lists the IUPAC names assigned to simple continuous-chain alkanes from C-1 to C-10. A common "ane" suffix identifies these compounds as alkanes. Longer chain alkanes are well known, and their names may be found in many reference and text books. The names methane through decane should be memorized, since they constitute the root of many IUPAC names. Fortunately, common numerical prefixes are used in naming chains of five or more carbon atoms.
| Name | Molecular Formula | Structural Formula | Isomers | Name | Molecular Formula | Structural Formula | Isomers | |
|---|---|---|---|---|---|---|---|---|
| methane | CH4 | CH4 | 1 | hexane | C6H14 | CH3(CH2)4CH3 | 5 | |
| ethane | C2H6 | CH3CH3 | 1 | heptane | C7H16 | CH3(CH2)5CH3 | 9 | |
| propane | C3H8 | CH3CH2CH3 | 1 | octane | C8H18 | CH3(CH2)6CH3 | 18 | |
| butane | C4H10 | CH3CH2CH2CH3 | 2 | nonane | C9H20 | CH3(CH2)7CH3 | 35 | |
| pentane | C5H12 | CH3(CH2)3CH3 | 3 | decane | C10H22 | CH3(CH2)8CH3 | 75 |
Some important behavior trends and terminologies: 
(i) The formulas and structures of these alkanes increase uniformally by a CH2 increment.
(ii) A uniform variation of this kind in a series of compounds is called homologous.
(iii) These formulas all fit the CnH2n+2 rule. This is also the highest possible H/C ratio for a stable hydrocarbon.
(iv) Since the H/C ratio in these compounds is at a maximum, we call them saturated (with hydrogen).
(ii) A uniform variation of this kind in a series of compounds is called homologous.
(iii) These formulas all fit the CnH2n+2 rule. This is also the highest possible H/C ratio for a stable hydrocarbon.
(iv) Since the H/C ratio in these compounds is at a maximum, we call them saturated (with hydrogen).
Beginning with butane (C4H10), and becoming more numerous with larger alkanes, we note the existence of alkane isomers. For example, there are five C6H14 isomers, shown below as abbreviated line formulas (A through E):
Although these distinct compounds all have the same molecular formula, only one (A) can be called hexane. How then are we to name the others?
The IUPAC system requires first that we have names for simple unbranched chains, as noted above, and second that we have names for simple alkyl groups that may be attached to the chains. Examples of some common alkyl groups are given in the following table. Note that the "ane" suffix is replaced by "yl" in naming groups. The symbol R is used to designate a generic (unspecified) alkyl group.
| Group | CH3? | C2H5? | CH3CH2CH2? | (CH3)2CH? | CH3CH2CH2CH2? | (CH3)2CHCH2? | CH3CH2CH(CH3)? | (CH3)3C? | R? |
| Name | Methyl | Ethyl | Propyl | Isopropyl | Butyl | Isobutyl | sec-Butyl | tert-Butyl | Alkyl |
30 Jan 2007 12:36:54 IST
Like
1 people liked this
IUPAC Rules for Alkane Nomenclature
1. Find and name the longest continuous carbon chain.
2. Identify and name groups attached to this chain.
3. Number the chain consecutively, starting at the end nearest a substituent group.
4. Designate the location of each substituent group by an appropriate number and name.
5. Assemble the name, listing groups in alphabetical order.
The prefixes di, tri, tetra etc., used to designate several groups of the same kind, are not considered when alphabetizing
2. Identify and name groups attached to this chain.
3. Number the chain consecutively, starting at the end nearest a substituent group.
4. Designate the location of each substituent group by an appropriate number and name.
5. Assemble the name, listing groups in alphabetical order.
The prefixes di, tri, tetra etc., used to designate several groups of the same kind, are not considered when alphabetizing
For the above isomers of hexane the IUPAC names are: B 2-methylpentane C 3-methylpentane D 2,2-dimethylbutane E 2,3-dimethylbutane
Halogen substituents are easily accomodated, using the names: fluoro (F-), chloro (Cl-), bromo (Br-) and iodo (I-). For example, (CH3)2CHCH2CH2Br would be named 1-bromo-3-methylbutane. If the halogen is bonded to a simple alkyl group an alternative "alkyl halide" name may be used. Thus, C2H5Cl may be named chloroethane (no locator number is needed for a two carbon chain) or ethyl chloride.
IUPAC Rules for Cycloalkane Nomenclature
1. For a monosubstituted cycloalkane the ring supplies the root name (table above) and the substituent group is named as usual. A location number is unnecessary.
2. If the alkyl sustituent is large and/or complex, the ring may be named as a substituent group on an alkane.
3. If two different substituents are present on the ring, they are listed in alphabetical order, and the first cited substituent is assigned to carbon #1. The numbering of ring carbons then continues in a direction (clockwise or counter-clockwise) that affords the second substituent the lower possible location number.
4. If several substituents are present on the ring, they are listed in alphabetical order. Location numbers are assigned to the substituents so that one of them is at carbon #1 and the other locations have the lowest possible numbers, counting in either a clockwise or counter-clockwise direction.
5. The name is assembled, listing groups in alphabetical order and giving each group (if there are two or more) a location number. The prefixes di, tri, tetra etc., used to designate several groups of the same kind, are not considered when alphabetizing.
2. If the alkyl sustituent is large and/or complex, the ring may be named as a substituent group on an alkane.
3. If two different substituents are present on the ring, they are listed in alphabetical order, and the first cited substituent is assigned to carbon #1. The numbering of ring carbons then continues in a direction (clockwise or counter-clockwise) that affords the second substituent the lower possible location number.
4. If several substituents are present on the ring, they are listed in alphabetical order. Location numbers are assigned to the substituents so that one of them is at carbon #1 and the other locations have the lowest possible numbers, counting in either a clockwise or counter-clockwise direction.
5. The name is assembled, listing groups in alphabetical order and giving each group (if there are two or more) a location number. The prefixes di, tri, tetra etc., used to designate several groups of the same kind, are not considered when alphabetizing.
Free Sign Up!
Preparing for JEE?
Kickstart your preparation with new improved study material - Books & Online Test Series for JEE 2014/ 2015
@ INR 4,950/-
For Quick Info
Find Posts by Topics
Physics
Topics
10271
20998
3866
2300
8075
2968
2788
Mathematics
Chemistry
Biology
Institutes
Parents Corner
Board
Fun Zone
|
Vertical Limit 
Top Contributors
All Time This Month Last Week | 1. |
|
Bipin Dubey
|
| 2. |
|
Himanshu
|
| 3. |
|
Hari Shankar
|
| 4. |
|
edison
|
| 5. |
|
Sagar Saxena
|
| 6. |
|
Yagyadutt Mishr..
|
| 35,229,755 Engineering Questions Attempted |
6,69,530 Visitors Monthly |
79 Engg. Exam Covered |
3980 Students Currently Online |
Connect with Us  |
 |
Vriti Communities
Privacy Policy © Vriti 2011