Nomenclature of organic compounds Questions in English

(N/A) $2,2,4-$Trimethylpentane
Condensed formula: $(CH_{3})_{3}CCH_{2}CH(CH_{3})_{2}$
Functional group: None (alkane)
$(b)$ $2-$Hydroxy$-1,2,3-$propanetricarboxylic acid
Condensed formula: $(HOOC)CH_{2}C(OH)(COOH)CH_{2}(COOH)$
Functional groups: Carboxylic acid $(-COOH)$ and alcoholic $(-OH)$ groups.
$(c)$ Hexanedial
Condensed formula: $OHC(CH_{2})_{4}CHO$
Functional group: Aldehyde $(-CHO)$ group.

(N/A) $(i)$ The longest chain contains $5$ carbon atoms. The parent alkane is pentane. Substituents are at positions $2, 2, 4, 4$. The name is $2,2,4,4-$Tetramethylpentane.
$(ii)$ The longest chain contains $5$ carbon atoms. The parent alkane is pentane. Substituents are at position $3, 3$. The name is $3,3-$Dimethylpentane.
$(iii)$ The structure is $C[C(CH_3)_3]_4$. The longest chain contains $9$ carbon atoms. The name is $3,3,7,7-$Tetramethyl$-5,5-$bis$(1,1-$dimethylethyl$)$nonane,commonly referred to as $3,3,5,5-$tetra$-tert-$butylpentane or based on the parent chain $2,2,4,4,8,8,10,10-$octamethyl$-6-(1,1-$dimethylethyl$)$undecane. However,the standard $IUPAC$ name for tetra$-tert-$butylmethane is $3,3,5,5-$tetra$-tert-$butylpentane.

(N/A) $(i)$ The structure of $2-Ethylpentane$ is $CH_3-CH(C_2H_5)-CH_2-CH_2-CH_3$. The longest chain contains $6$ carbon atoms,not $5$. Therefore,the correct $IUPAC$ name is $3-Methylhexane$.
$(ii)$ The structure of $5-Ethyl-3-methylheptane$ is $CH_3-CH_2-CH(CH_3)-CH_2-CH(C_2H_5)-CH_2-CH_3$. According to the lowest locant rule,numbering should start from the end that gives the lower number to the substituent. Therefore,the correct $IUPAC$ name is $3-Ethyl-5-methylheptane$.

(N/A) $(i)$ The longest chain containing both double bonds has $10$ carbons. Numbering from the left gives $2,8-$dimethyl$-3,6-$decadiene.
$(ii)$ The structure is $CH_2=CH-CH=CH-CH=CH-CH=CH_2$,which is $1,3,5,7-$octatetraene.
$(iii)$ The longest chain containing the double bond has $5$ carbons with a propyl group at position $2$. The name is $2-$propylpent$-1-$ene.
$(iv)$ The longest chain containing the double bond has $10$ carbons. Numbering from the left gives $4-$ethyl$-2,6-$dimethyl$-4-$decene.

(D) The $IUPAC$ names and bond counts for the given structures are as follows:

$(i)$ $CH_3-CH(CH_3)-CH=CH-CH_2-CH=C(CH_3)-CH_2-CH_3$	$2,7-\text{Dimethylnona}-3,6-\text{diene}$,$30 \sigma, 2 \pi$
$(ii)$ $CH_3-CH=CH-CH_2-CH=CH-CH(C_2H_5)-CH_2-CH_3$	$5-\text{Ethyldeca}-2,6-\text{diene}$,$33 \sigma, 2 \pi$
$(iii)$ $CH_2=C(CH_2-CH_2-CH_3)_2$	$2-\text{Propylpent}-1-\text{ene}$,$26 \sigma, 1 \pi$
$(iv)$ $CH_3-CH(C_4H_9)-CH=C(C_2H_5)-CH_2-CH(CH_3)_2$	$4-\text{Ethyl}-2,6-\text{dimethyldec}-4-\text{ene}$,$41 \sigma, 1 \pi$

(N/A) $a.$ $CH_3-CH=C(CH_3)_2$: The longest chain has $4$ carbons with a double bond at $C-2$ and a methyl group at $C-2$. $IUPAC$ name: $2-\text{Methylbut-}2-\text{ene}$.
$b.$ $CH_2=CH-C \equiv C-CH_3$: The chain has $5$ carbons. Double bond gets priority for numbering. $IUPAC$ name: $\text{Pent-}1-\text{en-}3-\text{yne}$.
$c.$ $CH_2=CH-CH=CH_2$: $IUPAC$ name: $\text{Buta-}1,3-\text{diene}$.
$d.$ $C_6H_5-CH_2-CH_2-CH=CH_2$: The principal chain is the alkene chain. $IUPAC$ name: $4-\text{Phenylbut-}1-\text{ene}$.
$e.$ $2-\text{Methylphenol}$: $IUPAC$ name: $2-\text{Methylphenol}$.
$f.$ $CH_3-(CH_2)_4-CH(CH_2-CH(CH_3)_2)-(CH_2)_3-CH_3$: Longest chain is $10$ carbons (decane). Substituent at $C-5$ is an isobutyl group $(2-\text{methylpropyl})$. $IUPAC$ name: $5-(2-\text{Methylpropyl})\text{decane}$.
$g.$ $CH_3-CH=CH-CH_2-CH=CH-CH(C_2H_5)-CH_2-CH=CH_2$: Longest chain with maximum double bonds is $10$ carbons. Numbering starts from the end closer to the first double bond. $IUPAC$ name: $4-\text{Ethyldeca-}1,5,8-\text{triene}$.

(N/A) $(i)$ $4-$Bromopent$-2-$ene
$(ii)$ $3-$Bromo$-2-$methylbut$-1-$ene
$(iii)$ $4-$Bromo$-3-$methylpent$-2-$ene
$(iv)$ $1-$Bromo$-2-$methylbut$-2-$ene
$(v)$ $1-$Bromobut$-2-$ene
$(vi)$ $3-$Bromo$-2-$methylprop$-1-$ene

(N/A) $(i)$ The longest chain containing the $-OH$ group has $5$ carbons. Numbering starts from the $-OH$ end. The name is $4-$chloro$-2,3-$dimethylpentan$-1-$ol.
$(ii)$ This is an ether. The longest chain is propane. The ethoxy group is at position $2$. The name is $2-$ethoxypropane.
$(iii)$ The structure shows a phenol ring with methyl groups at positions $2$ and $6$. The name is $2,6-$dimethylphenol.
$(iv)$ The ring is cyclohexane. The ethoxy group is at position $1$ and the nitro group is at position $2$ (alphabetical order). The name is $1-$ethoxy$-2-$nitrocyclohexane.

(A) $(i)$ $2-$Isopropyl$-3-$chloromethylpentan$-1-$ol
$(ii)$ $2,5-$Dimethylhexane$-1,3-$diol
$(iii)$ $3-$Bromocyclohexan$-1-$ol
$(iv)$ $Hex-1-$en$-3-$ol
$(v)$ $2-$Bromo$-3-$methylbut$-2-$en$-1-$ol

(N/A) $(i)$ $3-$Phenylpropanoic acid
$(ii)$ $3-$Methylbut$-2-$enoic acid
$(iii)$ $2-$Methylcyclopentanecarboxylic acid
$(iv)$ $2,4,6-$Trinitrobenzoic acid

(N/A) Complete structural formula (dash formula):
$(i)$ The covalent bond is represented by a dash $(-)$ or a small line.
$(ii)$ In the structure,every dash $(-)$ represents one bonding electron pair or two bonding electrons.
$(iii)$ $A$ single dash $(-)$ represents a single bond.
$(iv)$ $A$ double bond is represented by a double dash $(=)$.
$(v)$ $A$ triple bond is represented by a triple dash $(\equiv)$.
$(vi)$ Lone pairs of electrons on heteroatoms (e.g.,$O, N, S, X$ etc.) may or may not be shown.
$(vii)$ Every two atoms are connected by a dash $(-)$ to obtain the complete structure.
Example: Ethane $(CH_3-CH_3)$,Ethene $(CH_2=CH_2)$,Ethyne $(CH\equiv CH)$.
$(b)$ Condensed structural formula:
These structural formulas can be further abbreviated by omitting some or all of the dashes representing covalent bonds and by indicating the number of identical groups attached to an atom by a subscript.
$(i)$ In the structure,all single bonds indicated by dashes are not written.
$(ii)$ These formulas can be condensed by enclosing the repetitive structural unit within a bracket and placing an integer as a subscript indicating the number of times the structural unit is repeated.
$(iii)$ The multiple bonds present between $C$ and heteroatoms are also not written.
Example: $CH_3COCH_3$ is written instead of $CH_3-CO-CH_3$.
Example: The condensed structure of $CH_3-CH_2-CH_2-CH_2-CH_2-CH_2-CH_2-CH_3$ is written as $CH_3(CH_2)_6CH_3$.
$(c)$ Bond-line structural formula:
In this representation,carbon and hydrogen atoms are not shown,and the chain of carbon-carbon bonds is drawn as a zigzag line. The terminals of the line represent methyl groups $(CH_3)$,and the intersections represent methylene $(CH_2)$ or methine $(CH)$ groups. Heteroatoms are explicitly written.

(N/A) Nomenclature by $IUPAC$ method: Organic chemistry deals with millions of compounds. In order to clearly identify them,a systematic method of naming has been developed and is known as the $IUPAC$ system of nomenclature.
- $IUPAC$ stands for International Union of Pure and Applied Chemistry.
- Sometimes $IUPAC$ names are lengthy and complicated,so common names are used.
- In this systematic nomenclature,the names are correlated with the structure such that the reader or listener can deduce the structure from the name.
$(B)$ Trivial (common) nomenclature method: Organic compounds were assigned names based on their origin or certain properties.
- e.g.,Citric acid is named so because it is found in citrus fruits.
- The acid found in red ants is named formic acid since the Latin word for ant is $formica$.
- These names are traditional and are considered as trivial or common names.
- Some common names are followed even today. For example,Buckminster fullerene is a common name given to the newly discovered $C_{60}$ cluster (a form of carbon) noting its structural similarity to the geodesic domes popularized by the famous architect $R$. Buckminster Fuller.

(N/A) The $IUPAC$ nomenclature of organic compounds involves the following key steps:
$(i)$ Identification of the longest parent carbon chain.
$(ii)$ Identification of functional groups and substituents (branches) attached to the chain.
$(iii)$ Numbering the chain such that the principal functional group gets the lowest possible locant.
$(iv)$ Naming the compound by combining prefixes (substituents/branches),the parent alkane name,and the suffix (principal functional group).
For example,in the structure $CH_3-CH(CH_3)-CH_2-CH(Br)-CH(OH)-CH_3$,the parent chain is hexane,the principal functional group is $-OH$ (suffix $-ol$),and the substituents are $-Br$ (prefix bromo) and $-CH_3$ (prefix methyl). The correct name is $4$-bromo-$3$-methylhexan-$2$-ol.

(N/A) Number of carbon - Prefixes: The names of such compounds are based on their carbon-carbon chain length,which is determined by the number of carbon atoms.

$C_{1}$: Meth	$C_{8}$: Oct
$C_{2}$: Eth	$C_{9}$: Non
$C_{3}$: Prop	$C_{10}$: Dec
$C_{4}$: But	$C_{11}$: Undec
$C_{5}$: Pent	$C_{12}$: Dodec
$C_{6}$: Hex	$C_{20}$: Icos
$C_{7}$: Hept	$C_{30}$: Triacont

$(B)$ Alkanes containing $1$ to $10$ carbon atoms: The names are based on the chain structure with the suffix '-ane' and a prefix indicating the number of carbon atoms.
e.g.: If $4$ carbons are present,then 'But' + suffix 'ane' = Butane.
The general formula for alkanes is $C_{n}H_{2n+2}$.

Molecular Formula : Name	Molecular Formula : Name
$CH_{4}$ : Methane	$C_{7}H_{16}$ : Heptane
$C_{2}H_{6}$ : Ethane	$C_{8}H_{18}$ : Octane
$C_{3}H_{8}$ : Propane	$C_{9}H_{20}$ : Nonane
$C_{4}H_{10}$ : Butane	$C_{10}H_{22}$ : Decane
$C_{5}H_{12}$ : Pentane	$C_{20}H_{42}$ : Icosane
$C_{6}H_{14}$ : Hexane	$C_{30}H_{62}$ : Triacontane

(N/A) Propyl group:
$1$. $n$-Propyl group: $CH_3-CH_2-CH_2-$
$2$. Isopropyl group: $(CH_3)_2CH-$
$(b)$ Butyl group:
$1$. $n$-Butyl group: $CH_3-CH_2-CH_2-CH_2-$
$2$. Isobutyl group: $(CH_3)_2CH-CH_2-$
$3$. sec-Butyl group: $CH_3-CH_2-CH(CH_3)-$
$4$. tert-Butyl group: $(CH_3)_3C-$
$(c)$ Pentyl group:
$1$. $n$-Pentyl group: $CH_3-CH_2-CH_2-CH_2-CH_2-$
$2$. Isopentyl group: $(CH_3)_2CH-CH_2-CH_2-$
$3$. Neopentyl group: $(CH_3)_3C-CH_2-$

(A) The $IUPAC$ nomenclature system uses specific prefixes to denote the number of carbon atoms in the longest continuous chain:
$1$ carbon: $\text{Meth}$
$2$ carbons: $\text{Eth}$
$3$ carbons: $\text{Prop}$
$4$ carbons: $\text{But}$
$5$ carbons: $\text{Pent}$
$6$ carbons: $\text{Hex}$
$7$ carbons: $\text{Hept}$
$8$ carbons: $\text{Oct}$
$9$ carbons: $\text{Non}$
$10$ carbons: $\text{Dec}$
Therefore,the correct sequence is $1$: $\text{Meth}$,$2$: $\text{Eth}$,$3$: $\text{Prop}$,$4$: $\text{But}$,$5$: $\text{Pent}$,$6$: $\text{Hex}$,$7$: $\text{Hept}$,$8$: $\text{Oct}$,$9$: $\text{Non}$,$10$: $\text{Dec}$.

(N/A) The prefixes used in organic nomenclature represent the number of carbon atoms in the parent chain:
$1$. Meth: $1$ carbon atom
$2$. Prop: $3$ carbon atoms
$3$. Pent: $5$ carbon atoms
$4$. Hex: $6$ carbon atoms
$5$. Hept: $7$ carbon atoms

(A) $n$-propyl: $CH_3-CH_2-CH_2-$
$(b)$ Isopropyl: $(CH_3)_2CH-$
$(c)$ Isobutyl: $(CH_3)_2CH-CH_2-$
$(d)$ Isopentyl: $(CH_3)_2CH-CH_2-CH_2-$
Common feature in all $Iso$ groups: All $Iso$ groups contain a terminal $(CH_3)_2CH-$ structural unit.

(A) The prefix $Neo$ is used in the common system of nomenclature for alkanes that contain a quaternary carbon atom bonded to four other carbon atoms,where three of these are methyl groups attached to the same carbon atom.
An example of a $Neo$ alkane is $Neopentane$,which has the structure $CH_3-C(CH_3)_2-CH_3$ or $C(CH_3)_4$.

(A) secondary pentyl group is a $C_5H_{11}$ group where the point of attachment is a secondary carbon atom.
The structure $CH_3-CH_2-CH_2-CH(CH_3)-$ represents the $1$-methylbutyl group,which is a secondary pentyl group.
The structure $CH_3-CH_2-CH(CH_3)-CH_2-$ represents the $2$-methylbutyl group,which is a primary pentyl group.
Therefore,the correct structure for a secondary pentyl group among the options is $CH_3-CH_2-CH_2-CH(CH_3)-$,which corresponds to option $A$.

(N/A) The nomenclature of branched alkanes follows these rules:
Rule-$1$: Identify the longest carbon chain in the molecule,which is known as the 'parent chain'.
Example: In the structure $(II)$ below,the longest chain contains $9$ carbon atoms,whereas structure $(I)$ only contains $8$ carbon atoms. Thus,$(II)$ is the correct parent chain.
Rule-$2$: Number the carbon atoms of the parent chain to identify the parent alkane and locate the positions of substituents (alkyl groups). The numbering should be done such that the substituted carbon atoms get the lowest possible locants.
For example,in the structure $(a)$,numbering from left to right gives substituents at $C_2$ and $C_6$. In structure $(b)$,numbering from right to left gives substituents at $C_4$ and $C_8$. Since $2 < 4$,the numbering in $(a)$ is correct.
Rule-$3$: The names of the alkyl groups attached as branches are prefixed to the name of the parent alkane. The position of each substituent is indicated by its corresponding number. If different alkyl groups are present,they are listed in alphabetical order.

(A) The following table summarizes the common functional groups,their structures,prefixes,suffixes,and examples:
| Class of Compounds | Functional group structure | $IUPAC$ group prefix | $IUPAC$ group suffix | Example |
| :--- | :--- | :--- | :--- | :--- |
| Alkanes | $-$ | $-$ | $-ane$ | Butane,$CH_3(CH_2)_2CH_3$ |
| Alkenes | $>C=C<$ | $-$ | $-ene$ | But$-1-$ene,$CH_2=CHCH_2CH_3$ |
| Alkynes | $-C \equiv C-$ | $-$ | $-yne$ | But$-1-$yne,$CH \equiv CCH_2CH_3$ |
| Arenes | $-$ | $-$ | $-$ | Benzene |
| Halides | $-X$ $(X=F, Cl, Br, I)$ | $halo-$ | $-$ | $1-Bromobutane, CH_3(CH_2)_2CH_2Br$ |
| Alcohols | $-OH$ | $hydroxy-$ | $-ol$ | $Butan-2-ol, CH_3CH_2CHOHCH_3$ |
| Aldehydes | $-CHO$ | $formyl-$ or $oxo-$ | $-al$ | $Butanal, CH_3(CH_2)_2CHO$ |
| Ketones | $>C=O$ | $oxo-$ | $-one$ | $Butan-2-one, CH_3CH_2COCH_3$ |
| Nitriles | $-C \equiv N$ | $cyano-$ | $-nitrile$ | $Pentanenitrile, CH_3CH_2CH_2CH_2CN$ |
| Ethers | $R-O-R$ | $alkoxy-$ | $-$ | $Ethoxyethane, CH_3CH_2OCH_2CH_3$ |
| Carboxylic acids | $-COOH$ | $carboxy-$ | $-oic \ acid$ | $Butanoic \ acid, CH_3(CH_2)_2CO_2H$ |
| Carboxylate Ions | $-COO^-$ | $-$ | $-oate$ | $Sodium \ butanoate, CH_3(CH_2)_2CO_2Na^+$ |
| Esters | $-COOR$ | $alkoxycarbonyl$ | $-oate$ | $Methyl \ propanoate, CH_3CH_2COOCH_3$ |
| Acyl halides | $-COX$ $(X=F, Cl, Br, I)$ | $halocarbonyl$ | $-oyl \ halide$ | $Butanoyl \ chloride, CH_3(CH_2)_2COCl$ |
| Amines | $-NH_2, >NH, >N-$ | $amino-$ | $-amine$ | $Butan-2-amine, CH_3CHNH_2CH_2CH_3$ |
| Amides | $-CONH_2, -CONHR, -CONR_2$ | $carbamoyl-$ | $-amide$ | $Butanamide, CH_3(CH_2)_2CONH_2$ |
| Nitro compounds | $-NO_2$ | $nitro-$ | $-$ | $1-Nitrobutane, CH_3(CH_2)_3NO_2$ |
| Sulphonic acid | $-SO_3H$ | $sulpho-$ | $sulphonic \ acid$ | $Methylsulphonic \ acid, CH_3SO_3H$ |

(N/A) $(i)$ First of all,the functional group present in the molecule is identified,which determines the choice of the appropriate suffix.
$(ii)$ Longest parent chain: The longest chain of carbon atoms containing the functional group is numbered in such a way that the functional group is attached to the carbon atom possessing the lowest possible number in the chain.
$(iii)$ Polyfunctional compounds: In the case of polyfunctional compounds,one of the functional groups is chosen as the principal functional group,and the compound is then named on that basis. The remaining functional groups,which are subordinate,are named as substituents using appropriate prefixes.
$(iv)$ The choice of principal functional group is made on the basis of the order of preference. The order of decreasing priority for some functional groups is:
$-COOH > -SO_3H > -COOR > -COCl > -CONH_2 > -CN > -CHO > >C=O > -OH > -NH_2 > >C=C< > -C \equiv C-$
$(v)$ $-R, -C_6H_5$,halogens $(-F, -Cl, -Br, -I), -NO_2$,and alkoxy groups $(-OR)$ are always treated as prefix substituents.
$(vi)$ $A$ compound containing both an alcohol and a keto group is named as hydroxyalkanone since the keto group is preferred to the hydroxyl group. For example,$HOCH_2(CH_2)_3CH_2COCH_3$ is named as $7$-hydroxyheptan-$2$-one.
$(vii)$ If more than one functional group of the same type is present,their number is indicated by adding $di$,$tri$,etc.,before the class suffix. In such cases,the full name of the parent alkane is written before the class suffix. For example,$CH_2(OH)CH_2(OH)$ is named as ethane-$1,2$-diol.
$(viii)$ The ending $-e$ of the parent alkane is dropped in the case of compounds having more than one double or triple bond. For example,$CH_2=CH-CH=CH_2$ is named as buta-$1,3$-diene.

(N/A) Rule-$1$: For $IUPAC$ nomenclature of substituted benzene compounds,the substituent is placed as a prefix to the word benzene,as shown in the following examples:
| Compound | $IUPAC$ Name | Common Name |
| :--- | :--- | :--- |
| $C_6H_5CH_3$ | Methylbenzene | Toluene |
| $C_6H_5OCH_3$ | Methoxybenzene | Anisole |
| $C_6H_5C_2H_5$ | Ethylbenzene | - |
| $C_6H_5NH_2$ | Aminobenzene | Aniline |
| $C_6H_5OH$ | Hydroxybenzene | Phenol |
| $C_6H_5NO_2$ | Nitrobenzene | - |
| $C_6H_5Br$ | Bromobenzene | - |
| $C_6H_5SO_3H$ | Benzenesulphonic acid | -

(C) $(i)$ The ends represent methyl groups $(-CH_{3})$.
$(ii)$ Each corner represents a carbon atom. The number of hydrogen atoms attached to a carbon atom at a corner is determined by subtracting the number of bonds connected to that corner from $4$.

(A) The given structure is $CH_3-CH_2-C \equiv CH$ (but$-1-$yne).
In the skeletal structure,the left terminal carbon is involved in a triple bond $(C \equiv C)$,so it is bonded to only $1$ hydrogen atom $(CH \equiv C-)$.
The right terminal carbon is a methyl group $(-CH_3)$,so it is bonded to $3$ hydrogen atoms.
Therefore,the number of $H$ atoms attached to the terminal carbons are $1$ and $3$ respectively.

(A) $1$. Identify the longest carbon chain: The longest chain contains $8$ carbon atoms,so the parent alkane is octane.
$2$. Number the chain: Numbering from left to right gives substituents at positions $3$ (ethyl) and $6$ (methyl). Numbering from right to left gives substituents at positions $3$ (methyl) and $6$ (ethyl). Both sets of locants are $(3, 6)$.
$3$. Apply alphabetical order: When locant sets are the same,the substituent that comes first alphabetically receives the lower number. Since 'ethyl' comes before 'methyl',the ethyl group is assigned position $3$ and the methyl group is assigned position $6$.
$4$. Conclusion: The correct name is $3-$ethyl$-6-$methyloctane. Therefore,option $(i)$ is correct.

(A) The principal chain should be chosen such that it includes the substituent with more branching at the point of attachment.
Both $A$ and $B$ are alkyl groups with the same formula $C_{6}H_{13}$.
According to the $IUPAC$ rules for selecting the principal chain when two chains have equal length,the chain with more branching (or more complex branching) at the point of attachment is preferred.
In this case,the group $A$ has a quaternary carbon atom (a carbon bonded to four other carbons) at position $3$ of the substituent chain,which represents more branching compared to the structure of $B$.
Therefore,the chain containing $A$ should be selected as the principal chain.

(A) $1$. Identify the longest carbon chain. The longest chain contains $12$ carbon atoms,making it a dodecane derivative.
$2$. Number the chain to give the substituents the lowest possible locants. Starting from the right,the main chain is numbered $1$ to $12$.
$3$. At position $5$,there is a $2$-ethylbutyl group.
$4$. At position $3$ and $3$,there are two methyl groups.
$5$. Combining these,the $IUPAC$ name is $5-(2'-ethylbutyl)-3,3-dimethyldodecane$.

(N/A) The provided name is incorrect. According to $IUPAC$ rules,the principal chain must be the longest possible carbon chain. In the given structure,the longest chain contains $14$ carbon atoms,not $10$. The structure should be named as a derivative of tetradecane. Furthermore,when naming complex substituents,the chain attached to the main chain must be numbered starting from the point of attachment,and the longest chain within the substituent should be chosen.

(A) The structure is $CH_3-CH_2-CH(CH_2CH_3)-C(CH_3)_2-CH_2-CH_2-CH_3$.
$(i)$ If numbering starts from the left end,the substituents are at positions $3$ (ethyl) and $4,4$ (dimethyl). The name is $3$-ethyl-$4,4$-dimethylheptane.
$(ii)$ If numbering starts from the right end,the substituents are at positions $4,4$ (dimethyl) and $5$ (ethyl). The name is $5$-ethyl-$4,4$-dimethylheptane.
According to the $IUPAC$ rules,the set of locants $(3, 4, 4)$ is preferred over $(4, 4, 5)$ because $3 < 4$. Therefore,the numbering must start from the left end.

(9) To determine the longest parent chain,we identify the continuous chain of carbon atoms with the maximum number of atoms.
Looking at the structure:
$CH_3-CH(CH_3)-CH_2-CH_2-CH_2-CH(CH_2-CH_2-CH_3)-CH_2-CH_3$
If we follow the path labeled as $B$ in the image,the chain consists of $9$ carbon atoms.
Therefore,the longest parent chain contains $9$ carbon atoms.

(B) The given structure is $CH_3-CH(CH_3)-CH_2-CH_2-CH_2-CH(CH_2-CH_2-CH_3)-CH_2-CH_3$.
First,identify the longest carbon chain,which contains $9$ carbons (nonane).
Numbering the chain from the end that gives the lowest locants for substituents,we get substituents at positions $2$ and $6$.
The substituents are methyl $(-CH_3)$ and propyl $(-CH_2-CH_2-CH_3)$.
Wait,re-evaluating the structure: the substituent at position $6$ is a propyl group,not an ethyl group.
However,based on standard $IUPAC$ nomenclature rules,substituents must be listed in alphabetical order.
If the structure were $6-$ethyl$-2-$methylnonane,it would follow the alphabetical rule ($e$ before $m$).
Given the options,$(ii)$ is the correct choice as it follows the alphabetical ordering rule for naming substituents.

(A) The longest carbon chain contains $5$ carbon atoms,so the parent alkane is $pentane$.
There are two methyl groups attached at the $2^{nd}$ and $4^{th}$ carbon positions.
According to $IUPAC$ nomenclature rules,commas $(,)$ are used to separate numbers,and hyphens $(-)$ are used to separate numbers from letters.
The name should be written as a single word without spaces.
Therefore,the correct name is $2,4-Dimethylpentane$.

(N/A) The general formula of an alkyl group is $C_{n}H_{2n+1}$,which is denoted by $R$.
An alkyl group has one hydrogen atom less than the corresponding alkane group. Examples are shown in the table below:

Formula	Structure	Name
$CH_{3}-$	$-CH_{3}$	Methyl group
$C_{2}H_{5}-$	$CH_{3}-CH_{2}-$	Ethyl group
$C_{3}H_{7}-$	$CH_{3}-CH_{2}-CH_{2}-$	$n$-Propyl group
$C_{3}H_{7}-$	$CH_{3}-CH(CH_{3})-$	Isopropyl group
$C_{4}H_{9}-$	$CH_{3}-CH_{2}-CH_{2}-CH_{2}-$	$n$-Butyl group
$C_{4}H_{9}-$	$CH_{3}-CH_{2}-CH(CH_{3})-$	$sec$-Butyl group
$C_{4}H_{9}-$	$(CH_{3})_{2}CH-CH_{2}-$	Isobutyl group
$C_{4}H_{9}-$	$(CH_{3})_{3}C-$	$tert$-Butyl group

(N/A) The structure of neo-pentyl bromide is:
$CH_3-C(CH_3)_2-CH_2Br$
$IUPAC$ name: $1$-Bromo-$2,2$-dimethylpropane.

(N/A) The structure of glycerol is:
$CH_2OH-CHOH-CH_2OH$
The $IUPAC$ name of glycerol is $Propane-1,2,3-triol$.

(A) The longest carbon chain contains $6$ carbon atoms. The numbering starts from the right to give the lowest locants to the hydroxyl groups. The substituents are an ethyl group at position $3$ and a methyl group at position $5$. Thus,the name is $3$-ethyl-$5$-methylhexane-$2,4$-diol.
$(B)$ The structure is a cyclohexane ring. The methoxy group $(-OCH_3)$ and nitro group $(-NO_2)$ are substituents. Alphabetically,'methoxy' comes before 'nitro'. Numbering the ring to give the lowest locants,we get $1$-methoxy-$3$-nitrocyclohexane.

(D) $1.$ Identify the longest carbon chain containing both hydroxyl $(-OH)$ groups and the double bond. The longest chain has $5$ carbon atoms,so the parent alkane is pentane.
$2.$ Number the chain from the end that gives the $-OH$ groups the lowest possible locants. Numbering from the right gives the $-OH$ groups positions $1$ and $2$.
$3.$ $A$ methyl substituent is located at $C3$.
$4.$ The double bond starts at $C2$,making it $pent-2-ene$.
$5.$ Combining these,the $IUPAC$ name is $3-methylpent-2-ene-1,2-diol$.

(A-2, B-4, C-1, D-3) The matching is as follows:
$A \rightarrow 2$: The structure is $3$-bromocyclohexanol.
$B \rightarrow 4$: The structure $CH_3-C(Br)=C(CH_3)-CH_2OH$ is $2$-bromo-$3$-methylbut-$2$-en-$1$-ol.
$C \rightarrow 1$: The structure $CH_3-CH(CH_3)-CH_2-CH(OH)-CH(CH_2OH)-CH_3$ is $2,5$-dimethylhexane-$1,3$-diol.
$D \rightarrow 3$: The structure $CH_2=CH-CH(OH)-CH_2-CH_2-CH_3$ is hex-$1$-en-$3$-ol.
Therefore,the correct match is $(A-2, B-4, C-1, D-3)$.

(A-2, B-3, C-4, D-1) The matching is as follows:
$A$ ($1$-ethoxy-$2$-nitrocyclohexane) corresponds to structure $(2)$.
$B$ ($2,6$-dimethylphenol) corresponds to structure $(3)$.
$C$ ($2$-ethoxypropane) corresponds to structure $(4)$.
$D$ ($4$-chloro-$2,3$-dimethylpentan-$1$-ol) corresponds to structure $(1)$.
Thus,the correct matching is: $A$ $\rightarrow 2, B$ $\rightarrow 3, C$ $\rightarrow 4, D$ $\rightarrow 1$.

(A-V, B-IV, C-II, D-I, E-VI) The matching is as follows:
$(A)$ Cyclohexanol corresponds to $(v)$ Cyclohexanol.
$(B)$ $2$-methylcyclopentanol corresponds to (iv) $2$-methylcyclopentanol.
$(C)$ $3$-methylphenol corresponds to (ii) $3$-methylphenol.
$(D)$ $1$-ethoxy-$2,2$-dimethylcyclohexane corresponds to $(i)$ $2$-ethoxy-$1,1$-dimethylcyclohexane (Note: Numbering starts from the ethoxy group as $1$ in the $IUPAC$ name).
$(E)$ Benzene-$1,2,4$-triol corresponds to (vi) Benzene-$1,2,4$-triol.
Therefore,the correct matching is: $(A$ $\rightarrow v), (B$ $\rightarrow iv), (C$ $\rightarrow ii), (D$ $\rightarrow i), (E$ $\rightarrow vi)$.

(N/A) $3-$Phenylprop$-2-$enal
$(B)$ Cyclohexanecarbaldehyde
$(C)$ $3-$Oxopentanal
$(D)$ But$-3-$enal

(N/A) $CHO-CHO$ is Ethane$-1,2-$dial.
$(B)$ The structure is Benzene$-1,4-$dicarbaldehyde.
$(C)$ The structure is $3-$Bromobenzaldehyde.

(A) The structure of allyl amine is $CH_{2}=CH-CH_{2}-NH_{2}$.
In the $IUPAC$ nomenclature,the parent chain is a three-carbon alkene chain.
The double bond is at position $2$ and the amino group $(-NH_{2})$ is at position $1$.
Therefore,the $IUPAC$ name is $\text{prop-2-en-1-amine}$.

(N/A) $(1)$ For $CH_3-CH=C(CH_3)_2$,the longest chain contains $4$ carbon atoms. Numbering starts from the right to give the double bond and substituent the lowest possible locants. The $IUPAC$ name is $2-Methylbut-2-ene$.
$(2)$ For $CH_2=CH-C \equiv C-CH_3$,the longest chain contains $5$ carbon atoms. Numbering starts from the left to give the double bond priority over the triple bond when locants are equivalent. The $IUPAC$ name is $Pent-1-en-3-yne$.

(N/A) $(1)$ The compound $CH_2=CH-CH=CH_2$ is $buta-1,3-diene$.
$(2)$ The compound $C_6H_5-CH_2-CH_2-CH=CH_2$ is $4-phenylbut-1-ene$.
$(3)$ The compound with a benzene ring having $-OH$ at position $1$ and $-CH_3$ at position $2$ is $2-methylphenol$ (also known as $o-cresol$).

(A) $(1)$ The longest carbon chain contains $10$ carbon atoms. The substituent at position $5$ is a $2$-methylpropyl group. Thus,the $IUPAC$ name is $5-(2-methylpropyl)decane$.
$(2)$ The longest carbon chain containing the double bonds has $10$ carbon atoms. The substituent at position $4$ is an ethyl group. The double bonds are at positions $1, 5,$ and $8$. Thus,the $IUPAC$ name is $4-ethyldeca-1,5,8-triene$.

(N/A) The $neo$-pentyl group has the molecular formula $C_5H_{11}$.
It consists of a quaternary carbon atom bonded to three methyl groups and one methylene group $(-CH_2-)$,which acts as the point of attachment.
The structure is: $(CH_3)_3C-CH_2-$.

(N/A) $i$. Secondary-butyl group: $CH_3-CH_2-CH(CH_3)-$
$ii$. Tertiary-butyl group: $(CH_3)_3C-$