Q.Write the structure of the following organic halogen compound.
1, 4-Dibromobut-2-ene

2-chloro-3-methylpentane is a 5-carbon chain (pentane) with Cl on C2 and a methyl branch on C3.

Numbering the parent pentane chain C1 to C5:

• C1: CH₃
• C2: CHCl (chloro substituent here)
• C3: CH(CH₃) (methyl branch here)
• C4: CH₂
• C5: CH₃ …

But-2-ene is numbered C1-C4 with the double bond at C2=C3; substituting Br at C1 and C4 gives the structure.

Step 1: Draw the parent chain but-2-ene (4 carbons, double bond between C2 and C3):

CH3-CH=CH-CH3, numbered C1-C2=C3-C4.

Step 2: '1,4-dibromo' means a bromine substituent replaces one H each at C1 and C4.

Step 3: Combine — the structure is: …

Chloroform's structural formula is CHCl₃ and its IUPAC name is trichloromethane.

Chloroform is a haloalkane in which three of the four hydrogen atoms of methane (CH₄) are replaced by chlorine atoms.

Structural formula: three Cl atoms and one H atom attached to a single central carbon — written linearly as CHCl₃.

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The parent chain is pentane, bearing a chlorine and a methyl group on adjacent carbons; numbering from the end that gives the lower locant set names it 2-chloro-3-methylpentane.

Working out the IUPAC name

The given compound $CH_3-CH(Cl)-CH(CH_3)-CH_2-CH_3$ has a continuous 5-carbon chain, so the parent hydrocarbon is pentane.

Numbering from the left: C1 ($CH_3$), C2 (bears $Cl$), C3 (bears $CH_3$), C4 ($CH_2$), C5 ($CH_3$) $\to$ substituent locants {2 (chloro), 3 (methyl)}.

Numbering from the right instead would give locants {3 (methyl), 4 (chloro)}.

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IUPAC naming always starts by finding the LONGEST continuous carbon chain in the structure; here that chain runs through both ethyl branches (5 carbons, a pentane), leaving -CH3 and -CH2Br as two substituents on its middle carbon.

STRUCTURE: CH3-C(C2H5)2-CH2Br is a central carbon bonded to four groups: a -CH3, two -C2H5 (ethyl) groups, and a -CH2Br group. Total: 7 carbon atoms, 1 bromine.

STEP 1 - Find the longest chain: Tracing a path through the two ethyl branches AND the central carbon gives a continuous run of 5 carbons: CH3-CH2-C(...)-CH2-CH3. This is longer than the alternative path through the central carbon plus the -CH2Br arm (only 4 carbons). By the rule 'always select the longest possible continuous chain first,' the parent chain is this 5-carbon PENTANE, with the original central carbon becoming C-3 (the middle carbon, by symmetry).

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