Nomenclature of organic compounds Questions in English

(B) $1$. Identify the longest carbon chain containing the maximum number of carboxylic acid groups.
$2$. The structure is $HOOC-CH_2-CH(CH_2-COOH)-(CH_2)_3-COOH$.
$3$. The longest chain containing the three $-COOH$ groups is a heptane chain ($7$ carbons).
$4$. Numbering the chain starting from the end that gives the substituents the lowest locants: $1-COOH, 2-CH_2, 3-CH(CH_2-COOH), 4-CH_2, 5-CH_2, 6-CH_2, 7-COOH$.
$5$. At position $3$,there is a carboxymethyl group $(-CH_2-COOH)$.
$6$. The $IUPAC$ name is $3-(carboxymethyl)heptane-1,7-dioic acid$.

(D) $1$. Identify the principal functional group. The carboxylic acid group $(-COOH)$ has higher priority than the ketone group $(C=O)$.
$2$. Number the carbon chain starting from the carboxylic acid carbon as $C-1$.
$3$. The chain has $5$ carbons,so the parent alkane is pentane. The suffix for carboxylic acid is '-oic acid'.
$4$. The ketone group is at the $C-4$ position,so it is named as 'oxo'.
$5$. Combining these,the name is $4-\text{oxopentanoic acid}$.

(D) The given structure is $CH_3-CO-CH(CH_3)_2$.
First,identify the longest carbon chain containing the functional group (ketone).
The chain has $4$ carbon atoms,so the parent alkane is butane.
Numbering should be done from the side that gives the ketone group the lowest possible number.
Numbering from left to right: $CH_3(1)-CO(2)-CH(3)(CH_3)(4)$.
The ketone group is at position $2$ and a methyl group is at position $3$.
Therefore,the $IUPAC$ name is $3-$methylbutan$-2-$one or $3-$methyl$-2-$butanone.

(B) $1$. Identify the principal functional group or double bond. In a cyclic alkene,the double bond is given priority,and the carbons of the double bond are numbered $1$ and $2$.
$2$. To give the lowest possible locants to substituents,we number the ring starting from the double bond carbon attached to the chlorine atom as $1$,and the other double bond carbon as $2$. This makes the chlorine at position $1$.
$3$. Continuing the numbering around the ring,the bromine atom is at position $3$.
$4$. Thus,the name is $3-$bromo$-1-$chlorocyclohexene.

(D) $1$. Identify the longest carbon chain containing the functional group (chlorine) and substituents. The structure is $CH_3-C(CH_3)(CH_2CH_3)-CH_2-CH(Cl)-CH_3$.
$2$. The longest chain has $6$ carbon atoms (hexane).
$3$. Numbering should start from the end that gives the lowest locants to the substituents. Starting from the right,the chlorine is at $C-2$ and the methyl groups are at $C-4$.
$4$. The substituents are: $2-$chloro,$4,4-$dimethyl.
$5$. Combining these,the $IUPAC$ name is $2-$chloro$-4,4-$dimethylhexane.

(A) $1$. Identify the longest carbon chain containing the principal functional group $(-OH)$. The chain has $7$ carbons,so the parent alkane is $heptane$.
$2$. Number the chain from the end that gives the lowest locant to the principal functional group $(-OH)$. Numbering from left to right,$-OH$ is at $C-2$.
$3$. Identify substituents: Two $bromo$ groups are at $C-6$. The name is $6,6-dibromoheptan-2-ol$.

(B) The given structure is bicyclo$[2.2.1]$heptane,commonly known as norbornane.
To name a bicyclic compound,we identify the bridgehead carbons and count the number of carbon atoms in each of the three paths connecting them.
In this structure,there are two bridgehead carbons.
The three paths between these bridgehead carbons contain $2$,$2$,and $1$ carbon atoms respectively.
Therefore,the $IUPAC$ name is bicyclo$[2.2.1]$heptane,where the total number of carbon atoms is $2+2+1+2 = 7$ (heptane).

(A) $1$. Identify the longest carbon chain containing the functional group $(-OH)$. The chain has $5$ carbon atoms,so the parent alkane is $pentane$.
$2$. Number the chain from the end closer to the functional group $(-OH)$. The $-OH$ group is at $C-2$.
$3$. Identify the substituent: $A$ $methyl$ group $(-CH_3)$ is present at $C-4$.
$4$. Combine the parts: $4-$methylpentan$-2-$ol.

(B) $1$. Identify the longest carbon chain containing the double bond. The longest chain in the given structure has $10$ carbon atoms,making it a decene derivative.
$2$. Number the chain starting from the end that gives the double bond the lowest possible locant. Numbering from the right gives the double bond position at $C-4$.
$3$. Identify the substituents: there is an ethyl group at $C-5$ and $C-6$,and a methyl group at $C-3$.
$4$. Combining these,the $IUPAC$ name is $5,6-$diethyl$-3-$methyl$-4-$decene.

(B) The given structure is $(HOCH_2CH_2O)_2CH-COOH$.
$1$. Identify the principal functional group,which is the carboxylic acid group $(-COOH)$.
$2$. The parent chain is the ethanoic acid chain.
$3$. The substituent attached to the $C-2$ position is the $(HOCH_2CH_2O)-$ group,which is a $2-$hydroxyethoxy group.
$4$. Since there are two such groups attached to the same carbon atom $(C-2)$,the prefix used is $bis$.
$5$. Therefore,the $IUPAC$ name is $2,2-$bis$(2-$hydroxyethoxy$)$ethanoic acid.

(A) The given structure is a three-membered ring containing an oxygen atom,which is known as an oxirane or epoxide.
The ring carbons are numbered starting from one of the carbons bonded to oxygen.
There are two methyl groups attached to each of the two carbons of the oxirane ring.
Thus,the positions of the four methyl groups are at $2$ and $3$.
The correct $IUPAC$ name is $2,2,3,3-$tetramethyloxirane.

(D) The given structure is $CH_3-CH=CH-CH=CH-CH_3$.
Numbering from either end gives the double bonds at positions $2$ and $4$.
For the double bond at $C2$,the higher priority groups (the methyl group and the rest of the chain) are on opposite sides,which corresponds to the $E$ configuration.
For the double bond at $C4$,the higher priority groups are also on opposite sides,which corresponds to the $E$ configuration.
Therefore,the $IUPAC$ name is $(2E, 4E)-hexa-2,4-diene$.

(C) The given structure is $CH_2(CN)-CH(CN)-CH_2(CN)$.
In this compound,there are three $-CN$ groups attached to a propane chain.
According to $IUPAC$ nomenclature rules for compounds containing three or more identical functional groups (like $-CN$) attached to the same carbon skeleton,the carbon atoms of these functional groups are not included in the parent chain.
Therefore,the parent chain is propane,and the functional groups are named as 'carbonitrile'.
Since they are attached at positions $1, 2,$ and $3$,the correct name is $1,2,3-$propane tricarbonitrile.

(A) $1$. Identify the principal functional group,which is the carboxylic acid group $(-COOH)$.
$2$. The longest carbon chain must include the carbon of the $-COOH$ group.
$3$. Numbering starts from the $-COOH$ carbon as $C-1$.
$4$. The structure $CH_3-CH_2-CH_2-C(=O)-CH(CHO)-CH_2-CH_3$ contains a main chain of $7$ carbons when considering the longest continuous path including the principal functional group.

(A) $1$. Identify the longest carbon chain containing both the double and triple bonds. The chain has $5$ carbon atoms,so the parent name is 'pent'.
$2$. Number the chain starting from the end that gives the lowest locants to the multiple bonds. Numbering from the left gives the triple bond at $C-1$ and the double bond at $C-4$. Numbering from the right gives the double bond at $C-1$ and the triple bond at $C-4$.
$3$. According to $IUPAC$ rules,if there is a choice between a double and a triple bond,the double bond is given priority for the lower number. Thus,we number from the right: $CH_2=CH-CH_2-C\equiv CH$.
$4$. The double bond is at $C-1$ and the triple bond is at $C-4$. The name is Pent-$1$-en-$4$-yne.

(A) $1$. Identify the longest carbon chain containing both the double and triple bonds. The chain has $7$ carbons,so the parent alkane is heptane.
$2$. Number the chain from the end that gives the lower locant to the multiple bonds. Numbering from the right gives the triple bond at $C-1$ and the double bond at $C-5$. Numbering from the left gives the double bond at $C-2$ and the triple bond at $C-6$. Since $1 < 2$,we number from the right.
$3$. The substituents are a chloro group at $C-5$ and a methyl group at $C-4$.
$4$. Combining these,we get $5-\text{chloro}-4-\text{methylhept}-5-\text{en}-1-\text{yne}$.

(A) The given structure consists of a central carbon atom bonded to four phenyl groups $(-C_6H_5)$.
This compound is commonly known as tetraphenylmethane.
According to $IUPAC$ nomenclature,it is named as tetraphenylmethane,where methane is the parent alkane and there are four phenyl substituents attached to the central carbon atom.

(A) To name the compound $CH_3-C \equiv C-CH(CH_3)_2$ according to $IUPAC$ rules:
$1$. Identify the longest carbon chain containing the triple bond. The chain has $5$ carbons,so the parent alkane is pentane,and the alkyne is pentyne.
$2$. Number the chain from the end that gives the triple bond the lowest possible locant. Numbering from left to right,the triple bond starts at carbon $2$.
$3$. Identify the substituent. There is a methyl group $(-CH_3)$ attached to carbon $4$.
$4$. Combining these,the name is $4$-methylpent-$2$-yne or $4$-methyl-$2$-pentyne.

(A) $1$. Identify the longest carbon chain containing the functional group $(-COCl)$. The chain has $5$ carbons,so the parent alkane is pentane.
$2$. The functional group is an acyl chloride,so the suffix is $-oyl$ chloride. The parent name becomes pentanoyl chloride.
$3$. Number the chain starting from the carbon of the $-COCl$ group as $C-1$. The methyl group is at position $3$.
$4$. Combining these,the name is $3$-methylpentanoyl chloride.

(B) $1$. Identify the principal functional group: The carboxylic acid group $(-COOH)$ has higher priority than the ketone $(>C=O)$ and aldehyde $(-CHO)$ groups. Therefore,the parent chain is a cyclohexane ring with a carboxylic acid group at position $1$.
$2$. Number the ring: Start numbering from the carbon attached to the $-COOH$ group as $1$. To give the lowest possible locants to the other substituents,proceed clockwise: $C-1$ $(-COOH)$,$C-2$ $(-H)$,$C-3$ $(-C=O)$,$C-4$ $(-CHO)$,$C-5$ $(-H)$,$C-6$ $(-H)$. Wait,let's re-examine the structure: The $-COOH$ is at $C-1$,the ketone is at $C-3$,and the aldehyde is at $C-4$. Thus,the name is $4-$formyl$-3-$oxocyclohexane$-1-$carboxylic acid. However,looking at the options provided,option $B$ is the closest match for the structure where the aldehyde is treated as a substituent (formyl) and the ketone as an oxo group.

(B) $1$. Identify the longest carbon chain containing the double bond: The chain has $5$ carbons,so the parent alkane is pentene.
$2$. Number the chain starting from the end closer to the double bond: The double bond is at position $1$.
$3$. Identify the substituent: There is a methyl group at position $4$.
$4$. Combine the parts: The name is $4-$methylpent$-1-$ene.

(A) The given compound is a cyclic ketone with an ester functional group attached to the ring.
According to $IUPAC$ nomenclature rules,the ester group $(-COOC_2H_5)$ is treated as a substituent on the cyclopentanone ring.
The principal functional group is the ketone,so the ring is named as a cyclopentanone.
The carbon atom attached to the ester group is numbered $2$ relative to the ketone carbonyl carbon (which is $1$).
Thus,the name is ethyl $2$-oxocyclopentanecarboxylate.

(A) The given structure is a hydrocarbon chain with $5$ carbon atoms containing both a double bond and a triple bond.
According to $IUPAC$ nomenclature rules,when both double and triple bonds are present,the numbering is done such that the double bond gets the lower locant if there is a choice.
Numbering from the left: the triple bond is at position $1$ and the double bond is at position $4$.
Numbering from the right: the double bond is at position $1$ and the triple bond is at position $4$.
Since the double bond gets priority for the lower number,we number from the right.
Thus,the double bond is at position $1$ and the triple bond is at position $4$.
The parent chain has $5$ carbons,so it is a pentene-yne derivative.
The correct name is Pent-$1$-en-$4$-yne.

(B) The given structure is a cyclohexane ring attached to a $-COCl$ group.
According to $IUPAC$ nomenclature rules,when a functional group like $-CHO, -COOH, -COCl, -CN$,etc.,is directly attached to a ring,the carbon atom of the functional group is not included in the parent chain of the ring.
In such cases,a special suffix is used instead of the standard suffix.
For the $-COCl$ group attached to a ring,the suffix used is 'carbonyl chloride'.
Therefore,the parent ring is 'cyclohexane' and the functional group is 'carbonyl chloride',making the name 'Cyclohexanecarbonyl chloride'.

(A) $1$. Identify the longest carbon chain containing the functional group $(-NH_2)$ and the double bond $(C=C)$.
$2$. The chain has $3$ carbon atoms,so the parent alkane is propane.
$3$. Numbering starts from the carbon attached to the $-NH_2$ group to give it the lowest possible locant.
$4$. The double bond is at position $2$ and the amine group is at position $1$.
$5$. The name is $Prop-2-en-1-amine$.

(C) $1$. Identify the principal functional group: The aldehyde group $(-CHO)$ has the highest priority,so the suffix is $-al$ and the carbon of the $-CHO$ group is $C-1$.
$2$. Select the longest carbon chain containing the principal functional group and the maximum number of multiple bonds: The longest chain containing the $-CHO$ group,the double bond,and the triple bond is a $7$-carbon chain.
$3$. Numbering the chain: Start from the aldehyde carbon $(C-1)$. The double bond is at $C-2$ and the triple bond is at $C-6$.
$4$. Identify substituents: At $C-3$,there is a vinyl group $(-CH=CH_2)$.
$5$. Combine the parts: The parent chain is $hept-2-en-6-yn-1-al$. With the substituent,the name is $3-vinylhept-2-en-6-ynal$.

(D) $1$. Identify the principal functional group: The carboxylic acid group $(-COOH)$ has the highest priority,so the parent chain is a pentanoic acid derivative.
$2$. Number the chain starting from the carbon of the $-COOH$ group as $C-1$.
$3$. Identify substituents and their positions: The $-NO_2$ group is at $C-2$,the $-OH$ group is at $C-3$,and the ketone group $(=O)$ is at $C-4$.
$4$. Arrange substituents alphabetically: $H$ (hydroxy) comes before $N$ (nitro).
$5$. The name is $3-$hydroxy$-2-$nitro$-4-$oxopentanoic acid.

(A) $1$. Identify the principal functional group: The aldehyde group $(-CHO)$ has higher priority than the methoxy $(-OCH_3)$ and nitro $(-NO_2)$ groups. Therefore,the parent chain is benzaldehyde.
$2$. Number the ring: Start numbering from the carbon attached to the $-CHO$ group as $C-1$. Moving towards the substituents to give them the lowest possible locants,the methoxy group is at $C-2$ and the nitro group is at $C-4$.
$3$. Assemble the name: The substituents are $2-$methoxy and $4-$nitro. Alphabetically,'m' comes before 'n'.
$4$. Final name: $2-$methoxy$-4-$nitrobenzaldehyde.

(D) The given structure is a five-membered ring (cyclopentane) with three methyl groups attached to it.
To name it according to $IUPAC$ rules,we number the ring starting from one of the substituted carbons such that the set of locants is the lowest possible.
Starting from the top carbon as $1$,the methyl groups are at positions $1, 2,$ and $3$.
Thus,the name is $1, 2, 3-$trimethylcyclopentane.

(C) For the first compound: $CH_3-CH(OH)-CH_2-C(OH)(CH_3)_2$. The longest chain containing the functional groups has $5$ carbons. Numbering from the right gives the hydroxyl groups at positions $2$ and $4$,and a methyl group at position $2$. Thus,the name is $2-$methylpentane$-2,4-$diol.
For the second compound: $CH_2(CN)-CH(CN)-CH_2(CN)$. The three $-CN$ groups are attached to a $3-$carbon chain. The $IUPAC$ name for this is propane$-1,2,3-$tricarbonitrile.

(B) $1$. Identify the longest carbon chain. The longest chain contains $6$ carbon atoms (hexane).
$2$. Number the chain from the end that gives the substituents the lowest possible locants.
$3$. Numbering from left to right: substituents are at positions $2, 3, 4$.
$4$. Numbering from right to left: substituents are at positions $2, 3, 4$.
$5$. The substituents are two methyl groups at positions $2$ and $4$,and one ethyl group at position $3$.
$6$. Alphabetical order: $ethyl$ comes before $methyl$.
$7$. The correct $IUPAC$ name is $3-ethyl-2,4-dimethylpentane$.

(D) The given structure is $OHC-CH_2-CH(CHO)-CH_2-CHO$.
According to $IUPAC$ rules,when three or more identical functional groups are present,the carbon atoms of these groups are not included in the main chain.
Here,the main chain is propane,and the three aldehyde groups are attached to the $1, 2,$ and $3$ positions.
Therefore,the suffix used is 'tricarbaldehyde'.
The correct $IUPAC$ name is propane$-1, 2, 3-$tricarbaldehyde.

(A) The given structure is a skeletal representation. Expanding it,we have an ethyl group $(-CH_2CH_3)$ and a methyl group $(-CH_3)$ attached to a chain.
Following $IUPAC$ rules,we select the longest carbon chain.
The structure is $CH_3-CH(CH_3)-CH(CH_2CH_3)-CH_2-CH_3$.
The longest chain contains $6$ carbons (hexane).
Numbering from the side that gives the substituents the lowest locants,we get substituents at positions $2$ and $3$.
Thus,the name is $2, 3-$dimethylhexane.

(D) The given structure is $OHC-CH_2-CH(CHO)-CHO$.
To name this compound according to $IUPAC$ rules,we identify the longest carbon chain containing the principal functional groups.
Here,the three $-CHO$ groups are equivalent.
When three or more identical functional groups are present,the carbon atoms of these groups are excluded from the main chain,and the suffix 'carbaldehyde' is used.
The main chain consists of $3$ carbon atoms,which is 'propane'.
The positions of the $-CHO$ groups are at $C-1, C-2,$ and $C-3$.
Therefore,the $IUPAC$ name is $Propane-1,2,3-tricarbaldehyde$.

(A) $1$. Identify the longest carbon chain containing the double bond. The chain has $4$ carbon atoms,so the parent alkane is butane,and with the double bond,it is $1-$butene.
$2$. Number the chain starting from the end closer to the double bond. The double bond starts at carbon $1$.
$3$. Identify the substituents. There are two methyl groups at the $3^{rd}$ carbon position.
$4$. Combining these,the name is $3,3-$dimethyl$-1-$butene.

(B) $1$. Identify the longest carbon chain containing the principal functional group or the most substituents. Here,the longest chain is a butane chain ($4$ carbons).
$2$. Number the chain starting from the end that gives the substituent the lowest possible locant. The cyclopropyl group is attached to the $2^{nd}$ carbon.
$3$. The structure is a butane chain with a cyclopropyl group at the $2^{nd}$ position.
$4$. Therefore,the $IUPAC$ name is $2-$cyclopropylbutane.

(D) $1$. Identify the longest carbon chain containing the double bond. The longest chain has $5$ carbon atoms,so the parent alkane is pentane,and the alkene is pentene.
$2$. Number the chain from the end that gives the double bond the lowest possible locant. Numbering from the left,the double bond starts at carbon $2$.
$3$. Identify the substituents. There is a methyl group $(-CH_3)$ attached to carbon $3$.
$4$. Combining these,the name is $3-$methylpent$-2-$ene or $3-$methyl$-2-$pentene.

(B) The given structure consists of a cyclohexane ring fused to a cyclic anhydride group.
Specifically,it is a cyclic anhydride formed from cyclohexane-$1,2$-dicarboxylic acid.
According to $IUPAC$ nomenclature rules for cyclic anhydrides,the name is derived from the parent dicarboxylic acid by replacing the word 'acid' with 'anhydride'.
Therefore,the $IUPAC$ name is cyclohexane-$1,2$-dicarboxylic anhydride.

(C) In option $A$,the structure is $CH_3-CH(OH)-CH(CH_3)_2$. The longest chain has $4$ carbons,and the numbering starts from the end closer to the $-OH$ group,giving $3-$methylbutan$-2-$ol. This is correct.
In option $B$,$CH_3-C \equiv C-CH(CH_3)_2$ is $4-$methylpent$-2-$yne. This is correct.
In option $C$,the structure is $CH_3-CH_2-C(=CH_2)-CH_2-CH_3$. The longest chain containing the double bond has $5$ carbons,so it should be $2-$ethylpent$-1-$ene. The name $2-$ethylbut$-1-$ene is incorrect.
In option $D$,$3-$methyl$-4-$ethylheptane follows alphabetical order ($e$ before $m$),which is correct.

(C) $1$. Identify the longest carbon chain: The longest chain contains $7$ carbon atoms,so the parent alkane is $heptane$.
$2$. Number the chain: Numbering from the left gives substituents at positions $3, 5, 5$. Numbering from the right gives substituents at positions $3, 3, 5$. According to the lowest locant rule,we choose the numbering that gives the lowest set of locants ($3, 3, 5$ is lower than $3, 5, 5$).
$3$. Identify substituents: At position $3$,there are two methyl groups $(3, 3-\text{dimethyl})$. At position $5$,there is an isopropyl group $(5-\text{isopropyl})$.
$4$. Combine: The name is $5-\text{isopropyl}-3, 3-\text{dimethylheptane}$.

(B) According to the $CIP$ priority rules,priority is assigned based on the atomic number of the atom directly attached to the chiral center.
$1$. The atoms attached to the chiral carbon are $O$ (in $-OH$ and $-OCH_3$) and $C$ (in $-COOH$ and $-CHO$).
$2$. Since the atomic number of $O$ $(8)$ is greater than $C$ $(6)$,$-OH$ and $-OCH_3$ have higher priority than $-COOH$ and $-CHO$.
$3$. Comparing $-OH$ and $-OCH_3$: The $O$ in $-OCH_3$ is attached to a $C$ atom,while the $O$ in $-OH$ is attached to an $H$ atom. Comparing the next atoms,$C$ $(6)$ > $H$ $(1)$,so $-OCH_3$ has higher priority than $-OH$.
$4$. Comparing $-COOH$ and $-CHO$: The $C$ in $-COOH$ is bonded to $(O, O, O)$ (considering double bonds as two single bonds to $O$),while the $C$ in $-CHO$ is bonded to $(O, O, H)$. Comparing the atoms,$-COOH$ has higher priority than $-CHO$.
$5$. The final order is $-OCH_3 > -OH > -COOH > -CHO$.

(D) $1$. Identify the longest carbon chain containing the functional group ($-OH$ group). The chain has $6$ carbon atoms,so the parent alkane is hexane.
$2$. Number the chain from the end closer to the functional group $(-OH)$. Numbering from right to left gives the $-OH$ group at position $2$.
$3$. The substituent $-CH_3$ (methyl group) is located at position $5$ if numbered from right to left,but wait,let's re-examine the structure: $CH_3-CH(CH_3)-CH_2-CH(OH)-CH_3$.
$4$. Longest chain: $C_1(H_3)-C_2(H)(CH_3)-C_3(H_2)-C_4(H)(OH)-C_5(H_3)$ is a $5$-carbon chain (pentane).
$5$. Numbering from right: $C_1(H_3)-C_2(H)(OH)-C_3(H_2)-C_4(H)(CH_3)-C_5(H_3)$.
$6$. The substituent is at position $4$ (methyl) and the functional group is at position $2$ (ol). Thus,the name is $4-$methylpentan$-2-$ol.

(C) $1$. Identify the longest carbon chain containing the functional group $(-COOH)$ and the double bond $(C=C)$. The chain has $4$ carbons,so the parent alkane is butane.
$2$. Number the chain starting from the $-COOH$ carbon as $C-1$. Thus,$C-1$ is $-COOH$,$C-2$ is $=CH-$,$C-3$ is $=C(CH_3)-$,and $C-4$ is $-CH_3$.
$3$. The double bond starts at $C-2$,so it is a but$-2-$enoic acid derivative.
$4$. There is a methyl group at the $C-3$ position.
$5$. Combining these,the $IUPAC$ name is $3-$methylbut$-2-$enoic acid.

(B) The compound $NH_2-CO-NH_2$ is commonly known as urea.
According to $IUPAC$ nomenclature,the parent chain is based on the amide group.
The structure can be viewed as a methanamide derivative where one hydrogen atom is replaced by an amino group $(-NH_2)$.
Therefore,the $IUPAC$ name is $Aminomethanamide$.

(B) The given structure is $CH_3-CH_2-CH_2-CH(CH=CH_2)-CH_2-CH_2-CH_3$.
First,identify the longest carbon chain containing the double bond.
The longest chain has $6$ carbon atoms,making it a hexene derivative.
Numbering the chain from the end closer to the double bond gives the double bond position at $C-1$.
The substituent $-CH_2-CH_2-CH_3$ (propyl group) is attached at the $C-3$ position.
Thus,the $IUPAC$ name is $3$-propylhex-$1$-ene.

(C) The given compound is an ester derivative,specifically an alkyl chloroformate.
According to $IUPAC$ nomenclature rules for esters,the alkyl group attached to the oxygen is named first,followed by the name of the acyl group.
Here,the alkyl group is $C_2H_5$ (ethyl).
The acyl group is $Cl-C(=O)-$,which is derived from chloromethanoic acid (chloroformic acid).
Thus,the name is $Ethyl \ chloro \ methanoate$.

(B) To determine the $IUPAC$ name,we identify the parent chain and substituents.
$1$. The parent ring is benzene.
$2$. Substituents are chloro $(-Cl)$,nitro $(-NO_2)$,and methyl $(-CH_3)$.
$3$. According to $IUPAC$ rules,we number the ring to give the lowest possible locants to the substituents.
$4$. Alphabetical order is used for naming: chloro,methyl,nitro.
$5$. Assigning position $1$ to chloro,position $2$ to nitro,and position $4$ to methyl gives the set $(1, 2, 4)$.
$6$. Thus,the name is $1-$chloro$-4-$methyl$-2-$nitrobenzene.

(D) The structure is $C_6H_5-CH=CH-COOH$.
The principal functional group is the carboxylic acid $(-COOH)$,which gets the $C-1$ position.
The carbon chain consists of $3$ carbons,so the parent alkane is propane.
The double bond starts at $C-2$,so it is a prop-$2$-enoic acid derivative.
$A$ phenyl group $(-C_6H_5)$ is attached at the $C-3$ position.
Therefore,the $IUPAC$ name is $3$-phenylprop-$2$-enoic acid.

(B) $1$. Identify the principal functional group: The amide group $(-CONH_2)$ has the highest priority,so the parent chain is a butenamide derivative.
$2$. Number the chain starting from the amide carbon as $C-1$: $C-1$ is the carbonyl carbon of the amide,$C-2$ is the carbon with the double bond,$C-3$ is the carbon with the methoxy group,and $C-4$ is the carbon with the amino group.
$3$. Identify substituents: There is an amino group $(-NH_2)$ at $C-4$ and a methoxy group $(-OCH_3)$ at $C-3$.
$4$. Combine the parts: The compound is $4-amino-3-methoxy-2-butenamide$.

(D) $1$. Identify the principal functional group: Both groups are hydroxyl $(-OH)$ groups. Since they are equivalent,we look for the longest carbon chain or the ring.
$2$. The structure consists of a cyclohexane ring and a butyl chain. The ring is attached to the $2^{nd}$ carbon of the butyl chain.
$3$. Numbering the ring: The $-OH$ group on the ring gets priority $1$. The substituent $(-CH_2-CH(OH)-CH_2-CH_3)$ is at position $2$.
$4$. Numbering the chain: The chain is a butyl group. The $-OH$ group on the chain is at position $2$.
$5$. Combining these,the ring is $cyclohexan-1-ol$ and the substituent at position $2$ is a $2-\text{hydroxybutyl}$ group.
$6$. Thus,the correct $IUPAC$ name is $2-(2-\text{hydroxybutyl})\text{cyclohexan}-1-\text{ol}$.